Self-Aligned Structure and Method on Interposer-based PIC

ABSTRACT

Alignment aid structures and the method of formation of these structures on an interposer comprised of a planar waveguide layer and a base structure, facilitate the alignment of the optical axes of optical and optoelectrical devices formed from and mounted to the interposer. Alignment aids formed from a common hard mask on the planar waveguide layer of the interposer structure include vertical and lateral alignment structures and fiducials. Optical losses for signals propagating in interposer-based photonic integrated circuits are reduced with effective alignment structures and methods.

The present patent application is continuation from U.S. Utilityapplication Ser. No. 17/499,323, which claims priority from U.S.Provisional application Ser. No. 63/090,692, filed on Oct. 12, 2020,entitled “Self-Aligned Structure and Method on Interposer-based PIC”,hereby incorporated by reference in its entirety.

This application relates to U.S. patent application entitle Self-AlignedStructure and Method on Interposer-based PIC, filed on Oct. 12, 2021,Attorney docket number OPE-112B, hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to photonic integrated circuits and to theformation and method of use of alignment features that are formed on aninterposer-based optical planar waveguide structure. Alignment featuresinclude the formation of vertical and lateral reference structures thatfacilitate the alignment of optical components formed from the planarwaveguide layer of an interposer structure and to the alignment ofoptical components that are mounted onto the interposer. Such alignmentfeatures provide improvements in the manufacturability of photonicintegrated circuits (PICs) that use optical components formed from aplanar waveguide layer of an interposer structure and that to which diecan be mounted.

BACKGROUND

Developments in methods of manufacturing of photonic integrated circuits(PICs) have enabled the fabrication and integration of electrical,optoelectrical, and optical devices on the same substrate. In someapplications, pre-formed optoelectrical die are integrated within thePICs to provide functionality that may not be easily obtainable withsimilar devices formed directly on or within the substrate.Semiconductor lasers that emit signals at specific optical wavelengthssuited for optical communications, for example, are readily fabricatedfrom gallium arsenide and indium phosphide materials. The fabrication ofdevices that emit at these telecommunications wavelengths is notpractical or achievable using silicon or insulating substrates, and thusrequires the integration of pre-formed lasers into PIC mountingstructures. The integration of the optoelectrical die into PICs,however, requires precise placement and subsequent alignment afterplacement of optical and electrical features on the die with optical andelectrical features on the mounting substrate. Optical output from anintegrated laser die, for example, must align with optical planarwaveguides or other optical devices on the substrate to enable effectiveintegration of the laser with other devices in optoelectrical or opticalcircuits on the PIC substrate.

Effective alignment methodologies require the formation of alignmentstructures and strategies for which the alignment structures on mounteddie are compatible with alignment structures on the substrate ormounting structure and this compatibility can provide both technical andeconomic benefits in the manufacturing of PICs. Methodologies, forexample, that enable the implementation of passive alignment techniquesthat do not require direct feedback during the alignment process arepreferable over techniques and integration schemes that requirepotentially time-consuming active alignment steps. Effective integrationstrategies can also reduce coupling losses between devices, for example.The formation of the alignment structures or mechanical alignment aidsshould also be compatible with PIC fabrication techniques and methods,and suitable for high-volume production.

Thus, a need in the art exists for device structures and methods thatallow for passive integration of optoelectrical devices such assemiconductor lasers and photodiodes that provide suitable referencingschemes to enable effective alignment of integrated optoelectrical diewith waveguides and other features on the substrate during thefabrication of PICs.

SUMMARY

Embodiments of structures and methodologies are described herein for theformation and utilization of mechanical alignment aids that facilitatethe alignment of the optical planes of optical and optoelectricaldevices that are combined to form photonic integrated circuits (PICs)and the like. The alignment of the optical planes in these devices isrequired to facilitate the transference of optical signals between thedevices utilized in, or otherwise coupled to the PICs.

Alignment features are described in embodiments, herein, that includemechanical alignment aids formed on a substrate of a first optical oroptoelectrical device and on a mating device to vertically align acommon optical plane between two optical devices. Mechanical alignmentaids, as described herein, include vertical alignment pillars,fiducials, lateral constraints, and other alignment aids that are formedon a substrate to facilitate the alignment of the optical pathways oftwo or more optical devices. Alignment of the optical pathways, ingeneral, is required in PICs to facilitate the transfer of opticalsignals between devices in an optical circuit.

In an embodiment, a z-pillar is formed on a first optical oroptoelectrical device and brought into contact with a mechanicalreference surface that is formed on a second optical or optoelectricaldie to form and align a common horizontal optical signal plane betweenthe two optical devices. As used herein, the term “z-pillar” is used todescribe a structural pillar formed on a substrate or device that isused to establish a reference in “z” direction, a direction normal tothe flat surface plane of the substrate or device as described andreferenced herein. The reference height established by a z-pillar, insome embodiments, is the top surface of the z-pillar. In otherembodiments, other portions of the z-pillar are used to establish areference height of the z-pillar.

In embodiments described herein, the reference height of the z-pillar isformed with the use of a patterned first hard mask layer, wherein thefirst hard mask layer is formed from a material that is more resistiveto an etch or removal process than the surrounding material. A layer ofaluminum is formed over a material suitable for the formation of aplanar waveguide, such as one or more of silicon dioxide, siliconnitride, silicon oxynitride, or a combination of layers of thesematerials, for example, and is patterned to form the first hard mask forthe formation of a portion of z-pillars. A hard mask as used hereinrefers to a non-polymer-based material that is used to protectunderlying portions of a layer during a patterning process, for example.The patterned aluminum first hard mask layer, for example, protects theunderlying planar waveguide material in areas in which the aluminum ispresent, and allows the planar waveguide material to be removed fromareas in which the aluminum is not present. A selective etch process isused, for example, to remove the planar waveguide material that does notsubstantially etch the aluminum hard mask or other mask material. Theselective removal of the planar waveguide layer between the maskedaluminum areas results in the formation of a portion of the z-pillarsand other alignment aids as described herein. Aluminum is an effectivemask material for the formation of z-pillars when used in combinationwith fluorine-containing plasma etch chemistries such as thosecontaining SF₆, CHF₃, CF₄, C_(x)F_(y), among others. Other maskmaterials can also be used that provide a high selectivity for removalof the planar waveguide material relative to the more slowly etchedfirst mask material. Additional portions of the z-pillars can be formedin subsequent processes as described herein, in which the firstpatterned hard mask is buried in a layer of insulating dielectricmaterial, that is then patterned with a second hard mask layer. Thesecond hard mask is used in some embodiments to form a pattern for theformation of cavities, for example, that allow for the removal of theinsulating dielectric material layer and re-exposure of the buriedz-pillars that further allow for the formation of z-pillars that extendinto the layers below the planar waveguide layer.

In embodiments, a fiducial alignment feature is formed on a firstoptical or optoelectrical device and is used to establish a lateralalignment reference to facilitate the alignment of a second opticaldevice that is brought into proximity with, or mounted to, the firstoptical device. Formation of the fiducial and the z-pillars, in someembodiments, using the same hard mask patterning process, provides acommon focal plane to further facilitate alignment methods using thesefeatures. The hard mask, in some embodiments, is formed over the planarwaveguide layer of an interposer structure to further facilitatealignment of devices formed from the planar waveguide layer using thez-pillars and the fiducials.

In embodiments described herein, fiducial alignment features areillustrated as specific features formed for the purpose of providinglateral alignment reference. Embodiments in which a fiducial feature hasa secondary purpose within the structure of the PIC are also within thescope of embodiments. A fiducial, for example, formed from the hard masklayer may be a conductive element in the circuit, or may be a structuralfeature in the formation of the circuit.

In other embodiments, one or more z-pillar alignment features arecombined with one or more lateral fiducial features to form alignmentreferences in both the vertical and the lateral dimensions of twooptical or optoelectrical devices for which the vertical and lateraloptical planes are brought into alignment to enable the efficienttransfer of optical signals between the two aligned devices. And in yetother embodiments, the one or more z-pillar alignment features that arecombined with one or more lateral fiducial features are further combinedwith lateral constraints that are formed on one or both of the opticaldevices for which the vertical and lateral optical planes are broughtinto alignment to enable the transfer of optical signals between the twoaligned devices. The lateral constraints, in embodiments, restrict thelateral movement of the two combined optical or optoelectrical die andmaintain the lateral alignment of the optical pathways between the twodevices. These lateral constraints, in combination with the verticalalignment constraint that is provided by the one or more z-pillars,provide an effective structure for three-dimensional alignment of theoptical pathways between two or more optical devices.

Other aspects and features of embodiments will become apparent to thoseskilled in the art upon review of the following detailed description inconjunction with the accompanying figures.

DESCRIPTION OF THE DRAWINGS

FIG. 1 . Schematic drawings of (i) two optical devices with alignedoptical signal planes and (ii) two optical devices on a substrate withaligned optical signal planes.

FIG. 2 . Schematic drawings of (i) two optical devices shown withaligned optical signal planes in the z-direction and (ii) two opticaldevices on a substrate shown with aligned optical signal planes in thez-direction (perpendicular to the substrate surface as shown).

FIG. 3 . Schematic drawings of embodiments of two optical devices withaligned optical signal planes shown with mechanical alignment aid, az-pillar, to facilitate alignment in the vertical direction: (i) withoutan offset between the top of the z-pillar and the optical axes, and (ii)with an offset between the top of the z-pillar and the optical axis.

FIG. 4 . Schematic drawings of embodiments of an interposer structurethat includes a planar waveguide layer on a base structure for a basestructure that includes an electrical interconnect layer and asubstrate: (i) perspective view, (ii) cross section with detail providedfor the planar waveguide layer and the passivation layer, and (iii)cross section with detail provided for the electrical interconnect layerand with a mounted optical device in optical alignment with the planarwaveguide layer.

FIG. 5A. Schematic top-down and section drawings of two optical oroptoelectrical devices with aligned optical signal planes shown withmechanical alignment aid, a fiducial, to facilitate alignment in thelateral directions.

FIG. 5B. Schematic top-down and section drawings of two optical oroptoelectrical devices with aligned lateral and vertical optical signalplanes shown with a z-pillar mechanical alignment aid and a fiducial tofacilitate alignment in the lateral directions.

FIG. 5C. Schematic top down and section drawings of two optical oroptoelectrical devices with aligned lateral and vertical optical signalplanes shown with z-pillar mechanical alignment aids and a fiducialalignment aid to facilitate alignment in the lateral directions.

FIG. 6 . Embodiment of a method for forming and utilizing patternedalignment features on interposer substrate including die mounting of anoptoelectrical die on the interposer. In this embodiment, lateralalignment features are shown for alignment of the core of a fiber opticcable mounted in the v-groove with a planar waveguide formed from theplanar waveguide layer of the interposer.

FIG. 7A. Embodiment for a step of forming an interposer substrate.

FIG. 7B. Embodiment for a step of forming a patterned hard mask for theformation of planar waveguides, fiducial marks, z-pillars, and lateralalignment aids for the formation and alignment of a v-groove on aninterposer structure.

FIG. 7C. Embodiment for a step of patterning the planar waveguides,fiducial marks, v-groove alignment aids, and z-pillars on an interposerstructure.

FIG. 7D. Embodiment for a step of removing a hard mask layer from theplanar waveguides and optionally from features in the optical device.

FIG. 7E. Embodiment for a step of forming an insulating layer.

FIG. 7F. Embodiment for a step of forming a patterned hard mask for thecavity formation with z-pillars and for the formation of v-groovealignment aids (optionally exposing the fiducials).

FIG. 7G. Embodiment for a step of patterning the insulating layer toform cavities (with opening to optionally expose fiducials) and toexpose the v-groove alignment aids.

FIG. 7H. An embodiment for a step of patterning the insulating layer toform cavities for which a cavity is not formed to expose the fiducials.The v-groove alignment aids are exposed in this embodiment of thev-groove alignment aids.

FIG. 7I. Embodiment for a step of removing a hard mask layer afterformation of the cavity (embodiments shown in which the fiducials areexposed).

FIG. 7J. Embodiment for a step of forming a mask layer to facilitateformation of one or more v-grooves.

FIG. 7K. Embodiment for a step of forming one or more v-grooves and forremoving the mask layer after formation of the v-grooves.

FIG. 7L. Embodiment showing a fiber optic cable positioned in av-groove.

FIG. 7M. Perspective schematic drawing of an embodiment of anoptoelectrical device or die with a facet that has an optical axis foralignment with optical devices on an interposer.

FIG. 7N. Perspective drawing of an embodiment of an interposer structurehaving hard mask patterned planar waveguides, fiducial marks, z-pillars,and v-groove lateral alignment aids after z-pillar formation in aninterposer cavity, and after placement of a first optoelectrical dieinto the interposer cavity.

FIG. 7O. Perspective drawing of an embodiment of an interposer structurehaving hard mask patterned planar waveguides, fiducial marks, z-pillars,and v-groove lateral alignment aids after z-pillar formation in aninterposer cavity, and placement of a first and second optoelectricaldie into the interposer cavity.

FIG. 7P. Perspective drawing of an embodiment of an interposer structurehaving hard mask patterned planar waveguides, fiducial marks, z-pillars,and v-groove lateral alignment aids after z-pillar formation ininterposer cavity, placement of the first and second optoelectrical die,and after final positioning of a first and second optoelectrical die inan embodiment with two optoelectrical die.

FIG. 7Q. An example alignment process for a die mounted in a cavity onan interposer that includes the following steps: (i) Positioning of anoptical device over a cavity in the interposer, (ii) placement of theoptical device into the cavity, (iii) lateral alignment of the device inthe cavity with initial heating and melting of the solder connection,and (iv) after alignment and contact formation.

FIG. 7R. (i) Schematic top-down drawing showing the position of a dieafter placement into a cavity on an embodiment of an interposer withalignment aids and showing the position of the die after alignment andcontact formation using solder melting to align the die to the planarwaveguide, (ii) schematic side view of the embodiment.

FIG. 7S. Example apparatus for heating of the solder connections betweenthe mounted die and the interposer after placement to melt the solderconnections and to align an optical device to optical feature on theinterposer (i) heating of the substrate, (ii) heating of the substrateand radiative heating from above the substrate, (iii) laser heating ofthe solder connection through the substrate, (iv) heating of thesubstrate and heating of the die, (v) heating of the ambient.

FIG. 7T. Example of an embodiment of a die on an interposer after reflowheating of the solder connections to melt the solder connections toalign optoelectrical die to interposer features.

FIG. 8A. Embodiments of two optical or optoelectrical devices withaligned optical signal planes: (i) cross section, (ii) top-down viewwith single pillar and fiducial, and (iii) top-down view with twopillars and fiducial.

FIG. 8B. Embodiments of two optical or optoelectrical devices withaligned optical signal planes: (i) cross section, (ii) top-down viewwith three pillars, (iii) top-down view with four pillars, and (iv)top-down view with five pillars.

FIG. 8C. Embodiments of two optical or optoelectrical devices withaligned optical signal planes: (i) cross section, (ii) top-down viewwith six pillars, (iii) top-down view with seven pillars.

FIG. 9A. Embodiments of two optical or optoelectrical die with alignedoptical signal planes shown with z-pillar mechanical alignment aids, afiducial alignment aid, and lateral constraints: (i) top-down view and(ii) Section A-A′.

FIG. 9B. Embodiments of two optical or optoelectrical devices withaligned lateral and vertical optical signal planes shown with z-pillarmechanical alignment aids, a fiducial alignment aid, and lateralconstraints to facilitate alignment of the optical signal planes in thevertical and lateral directions.

FIG. 9C. (i)-(xii) Top-down views of embodiments of patterned interposeralignment pillars with complementary mechanical alignment aids onoptoelectrical die. (Note: shaded areas 934 are shaped z-pillars on theinterposer.)

FIG. 10A. Perspective drawings of an embodiment showing (i) opticaldevice with alignment features, (ii) portion of interposer with z-pillarstructures, and (iii) optical device with alignment features mounted inportion of the interposer with complementary alignment pillars (solidlines are the interposer substrate with alignment pillars and dottedlines are the mounted optical die with alignment features. In thisembodiment, the interposer pillars are positioned within the mechanicalfeatures of the optoelectrical die.

FIG. 10B. An embodiment of an optoelectrical die mounted on aninterposer substrate with mechanical alignment pillars formed on theinterposer and on the optoelectrical die. In this embodiment, theinterposer pillars are positioned within the mechanical features of theoptoelectrical die. (i) after placement of the optoelectrical die ontothe interposer substrate, prior to final positioning, and (ii) afterpositioning of the optoelectrical die on the interposer.

FIG. 11A. Perspective drawings of an embodiment showing (i) opticaldevice with alignment features, (ii) portion of interposer with z-pillarstructures, and (iii) optical device with alignment features mounted inportion of the interposer with complementary alignment pillars (solidlines are the interposer substrate with alignment pillars and dottedlines are the mounted optical die with alignment features.

FIG. 11B. An embodiment of an optical device mounted on an interposersubstrate with mechanical alignment pillars formed on the interposer andon the optical device. In the embodiment, the interposer pillars arepositioned outside of the mechanical features of the optical device: (i)after placement of the optoelectrical die onto the interposer substrate,prior to final positioning, and (ii) after positioning of theoptoelectrical die on the interposer substrate.

FIG. 11C. Perspective drawing of an embodiment showing an optical devicemounted over alignment pillars in an interposer cavity with theoptoelectrical device in alignment with a planar waveguide of theinterposer (the interposer and cavity are shown in solid lines and theoptical device is shown with dotted lines).

FIG. 12A. Perspective drawings of an embodiment showing (i) opticaldevice with alignment features, (ii) portion of interposer with z-pillarstructures, and (iii) optical device with alignment features mounted inportion of the interposer with complementary alignment pillars (solidlines are the interposer substrate with alignment pillars and dottedlines are the mounted optical die with alignment features.

FIG. 12B. An embodiment of an optoelectrical die mounted on aninterposer substrate with mechanical alignment pillars formed on theinterposer and on the optoelectrical die: (i) after placement of theoptoelectrical die onto the interposer substrate, and (ii) afterpositioning and alignment of the optoelectrical die on the interposer.

FIG. 12C. Perspective drawing of an embodiment showing the opticalfeatures of a mounted optical device with alignment features, alignedwith the optical facet of a planar waveguide on the interposer. Theoptical device is mounted on alignment pillars in the interposer cavitywith the optoelectrical device in alignment with the planar waveguide ofthe interposer (the interposer and cavity are shown in solid lines andthe optoelectrical die is shown in dotted lines).

FIG. 12D. Perspective drawings of an embodiment showing (i) a discreteoptical device with alignment features that are patterned to align withshaped pillars in the interposer cavity in (ii). Four of the discretedevices depicted in the embodiment shown in (i) can be mounted in theInterposer cavity shown in (ii). Exposed facets of multiple planarwaveguides are also shown.

FIG. 12D (continued). (iii) Perspective drawing of an embodiment showingfour discrete devices mounted in a cavity on an interposer and alignedwith exposed facets of multiple planar waveguides. Four optical devicesare mounted over the alignment pillars in the interposer cavity with theoptoelectrical devices in substantial alignment with the planarwaveguides of the interposer (the interposer and cavity are shown insolid lines and the optoelectrical die is shown in dotted lines).

FIG. 12E. Perspective drawings of an embodiment showing (i) an opticaldie formed with four devices and alignment features that are patternedto align with shaped pillars on an interposer configured as shown in(ii). (ii) an embodiment showing patterned pillars formed in a cavity onan interposer for a multi-device optical die with exposed facets ofmultiple planar waveguides.

FIG. 12E (continued). Perspective drawing of an embodiment showing a diewith four optical devices and with patterned alignment pillars that ismounted in an interposer cavity. The emitting or receiving facets of thedie containing four optoelectrical devices are shown aligned withexposed facets of planar waveguides embedded in the interposer structure(the interposer and cavity are shown in solid lines and theoptoelectrical die is shown in dotted lines).

FIG. 12F. Perspective drawing of an embodiment showing a die with fouroptical devices and with patterned alignment pillars that is mounted inan interposer cavity. The alignment features are shown in the embodimentat the edge of the mounted die and the corresponding locations in theinterposer cavity. The emitting or receiving facets of theoptoelectrical devices are shown aligned with exposed facets of planarwaveguides embedded in the interposer structure (the interposer andcavity are shown in solid lines and the optoelectrical die is shown indotted lines).

FIG. 13A. Embodiment of a process flow for forming a z-pillar in acavity.

FIG. 13B. Embodiment of a process flow for forming a structure withz-pillars at two heights in a cavity.

FIG. 13C. Embodiment of a process flow for forming a structure withz-pillars at multiple heights in a cavity.

FIG. 13D. Embodiment of a process flow for forming a z-pillar in anembodiment without a cavity.

FIG. 13E. Embodiment with z-pillars formed at multiple heights. In thisembodiment, the highest z-pillar is formed in alignment (from the samemask layer) as the planar waveguide layer and the fiducial.

FIG. 14 . Embodiment of alignment structure with dual z-pillar heightsshown with two planar waveguide layers. Each of the planar waveguidelayers is shown in alignment with a z-pillar and a fiducial: (i)top-down, and (ii) side view.

FIG. 15A. Embodiments of two optical devices with aligned optical signalplanes shown with mechanical alignment aid, a z-pillar, to facilitatealignment in the vertical direction: (i) optical device formed on asubstrate with an offset between the optical axis and the top of thesubstrate and with an offset between the top of the z-pillar and theoptical axis, and (ii) with an offset between the optical axis and thetop of the z-pillar, the top of the substrate, and a reference plane indevice.

FIG. 15B. Embodiments of two optical devices with aligned optical signalplanes shown with z-pillar mechanical alignment aids formed on surfacepillars to facilitate alignment: (i) optical devices formed on asubstrate with an offset between the optical axis and the top of thez-pillars, (ii) optical devices formed on a substrate with differingoffsets between the optical axis and the top of the z-pillars.

FIG. 15B (continued). Embodiments of two optical devices with alignedoptical signal planes shown with z-pillar mechanical alignment aidsformed on surface pillars to facilitate alignment: (iii) optical devicesformed on a substrate with multiple offsets between the optical axis andthe top of the z-pillars, and (iv) optical devices formed on a substratewith a single offset between the optical axis and the top of thez-pillars for a device and multiple offsets between the optical axis andthe top of the z-pillars for another device.

FIG. 15C. Embodiments of two optical devices with aligned optical signalplanes shown with z-pillar mechanical alignment aids formed in cavitiesin substrate to facilitate alignment: (i) optical devices formed with anoffset between the optical axis of the PIC and the top of the z-pillars,(ii) optical devices formed with an intermediate waveguide on thesubstrate between the devices with an offset between the PIC opticalaxis and the top of the z-pillars.

FIG. 15C (continued). Embodiments of two optical devices with alignedoptical signal planes shown with z-pillar mechanical alignment aidsformed in cavities in substrate to facilitate alignment: (iii) opticaldevices formed with an intermediate waveguide within the substrate withan offset between the optical axis and the top of the z-pillars, and(iv) optical devices formed with an intermediate waveguide within thesubstrate with multiple offsets between the optical axis and the top ofthe z-pillars

FIG. 15D. Embodiments of two optical devices with aligned optical signalplanes shown with z-pillar mechanical alignment aids in which thealigned devices are mounted over the pillars to form a contact with thebottom surface of a cavity formed in the substrate with (i) waveguideformed on the surface, and (ii) with waveguide formed in the substrate.

FIG. 15E. (i) Embodiments of two optical devices with aligned opticalsignal planes shown with z-pillar alignment aids and with an edgemounted device, and (ii) edge mounted device aligned on z-pillar shownin alignment with a planar waveguide, and (iii) an example of a type ofedge mounted fiber optic cable mounting block.

FIG. 15E (continued). Embodiments of two optical devices with alignedoptical signal planes shown with z-pillar alignment aids for an edgemounted device in which (iv) the z-pillar of the edge mounted device isformed in a cavity, and in which (v) both devices are mounted onz-pillars formed in cavities

FIG. 15F. Embodiments of two optical devices with aligned optical signalplanes shown with z-pillar mechanical alignment aids in which one of thedevices is a ball lens in alignment with (i) a device mounted over az-pillar formed in a cavity, and (ii) a device mounted over a z-pillarformed in a cavity and with a planar waveguide between the two opticaldevices.

FIG. 16 . Embodiment of alignment aids for which z-pillars to providez-alignment of the optical plane of two optical devices, namely, amounted die and a planar waveguide are formed concurrently.

FIG. 17 . Embodiment in which the z-pillar, a planar waveguide layer,and a fiducial are formed concurrently (hard mask for the planarwaveguide 1744 in the interposer is not shown) to provide z-alignment ofthe optical plane of two optical devices, namely, a mounted device andan waveguide in an interposer. Co-formation of the fiducial is used inthis embodiment for precision alignment in the lateral directions (x &y).

FIG. 18A. Two mounted optical devices with planar waveguide shown withaligned optical signal planes. Alignment aids to facilitate alignmentinclude the co-formed planar waveguide, z-pillars, and fiducial.Z-pillars in the embodiment shown are at a common height. (i) withz-pillars and fiducial formed in cavities, and (ii) with z-pillars andfiducial formed without cavities.

FIG. 18B. A mounted optical device shown in optical alignment with anoptical device formed on the interposer. The planar waveguide layer isused in the formation of the z-pillars, the optical device, and thefiducial. Alignment aids to facilitate alignment include the z-pillarsand the fiducial formed with the optical device. The z-pillars in theembodiment shown are at a common height.

FIG. 18C. Two mounted optical devices shown with aligned optical signalplanes. Alignment aids to facilitate alignment include the co-formedz-pillars and fiducial. Z-pillars in the embodiment shown are at acommon height. (i) with z-pillars and fiducial formed in cavities, and(ii) with z-pillars and fiducial formed without cavities.

FIG. 18D. Two mounted optical devices shown with aligned optical signalplanes. Alignment aids to facilitate alignment include the co-formedz-pillars and fiducial. (i) z-pillars are at different heights for thetwo devices, (ii) z-pillars are at multiple heights within each of thetwo devices, and (iii) z-pillars are at the same height for one of thedevices and at multiple heights for another of the devices.

FIG. 18E. Two mounted optical devices shown with aligned optical signalplanes for which one of the devices is a ball lens. Alignment aids tofacilitate alignment include the co-formed z-pillars and fiducial. (i)co-formed z-pillars and fiducial are at a different height than theoptical plane, (ii) co-formed z-pillar and fiducial are at the sameheight as the optical plane and shown with a planar waveguide also withaligned optical plane, and (iii) co-formed z-pillar and fiducial are atthe same height as the optical plane and shown with a third device alsowith aligned optical plane.

FIG. 19 . Embodiment in which the z-pillar, a planar waveguide layer,and a fiducial are formed concurrently to provide z-alignment of theoptical plane of two optical devices, namely, a mounted device and awaveguide in an interposer. Co-formation of the fiducial is used in thisembodiment for precision placement and alignment in the lateraldirections (x & y). Also shown is a lateral constraint feature in themounted device to constrain movement in the lateral directions (x & y).The lateral constraint feature is a capturing feature.

FIG. 20 . (i) Section view and (ii) top-down view of an embodiment of analignment aid co-formed with the fiducial and the planar waveguide layerfor alignment of a v-groove for mounting a fiber optic cable to a PIC.The co-formation of the v-groove alignment aid provides lithographiclevel positioning accuracy between the v-groove and the planar waveguideto which the core of the fiber cable is aligned.

FIG. 21 . Co-formed fiducial, z-pillars, planar waveguide, and alignmentaid for an embodiment with a fiber optic cable mounting block. Theco-formation of the fiber block alignment aid provides lithographiclevel positioning accuracy between the fiber block and the planarwaveguide to which the core of the fiber cable is aligned. The z-pillarsshown in the embodiment provide reference for the fiber mounting block.

FIG. 22 . Co-formed fiducial, z-pillars, and alignment aid for anembodiment with a fiber optic cable mounting block. Z-pillars shown inthe embodiment provide reference for a mounted die and other z-pillarsshown in the embodiment provide reference for the fiber mounting block.The co-formation of the fiber block alignment aid provides lithographiclevel positioning between the core of the fiber in the fiber mountingblock and the optical axis of the mounted device.

FIG. 23 . Embodiment of a method for forming and utilizing patternedalignment features on interposer substrate with mounted device and thatincludes v-grooves that can be used in embodiments with and without afiber optic mounting block.

FIG. 24A. Embodiment of a step of forming an interposer substrate.

FIG. 24B. Embodiment of a step of forming a patterned hard mask for theformation of planar waveguides, fiducial marks, and pillars on aninterposer structure.

FIG. 24C. Embodiment of a step of patterning planar waveguides, fiducialmarks, v-groove alignment aids, and pillars on an interposer structure.

FIG. 24D. Embodiment of a step of removing a hard mask layer from theplanar waveguides and optionally from features in the optical device.

FIG. 24E. Embodiment of a step of forming an insulating layer.

FIG. 24F. Embodiment of a step of forming a patterned hard mask tofacilitate the formation of cavities with z-pillars for the mounted die,the fiducials, and the fiber cable mounting block.

FIG. 24G. Embodiment of a step of forming cavities for mounted devices,for fiducial, and for fiber optic cable mounting block.

FIG. 24H. Embodiment of a step of removing hard mask after formation ofthe cavities.

FIG. 24I. Embodiment of a step of forming a v-groove on the interposer.(Figure shows a portion of a fiber optic cable positioned in the formedv-groove.)

FIG. 24J. Perspective view of an embodiment that includes a portion of afiber optic cable mounted in a fiber optic cable mounting block and withfiber optic cable mounting block positioned on the PIC.

FIG. 25 . An embodiment of a method for forming and utilizing patternedalignment features on an interposer substrate with mounted device andwith fiber optic mounting block. In these embodiments, z-pillaralignment features are formed on the interposer for alignment of thecore of the fiber optic cable in the fiber mounting block to waveguidesor other optical devices on the interposer.

FIG. 26A. Embodiment of a step of forming an interposer substrate.

FIG. 26B. Embodiment of a step of forming a patterned hard mask for theformation of planar waveguides, fiducial marks, z-pillars for diemounting and alignment, and z-pillars for fiber block mounting andalignment on an interposer structure.

FIG. 26C. Embodiment of a step of patterning the planar waveguides,fiducial marks, z-pillars for the die mounting, and z-pillars for thefiber block mounting on an interposer structure.

FIG. 26D. Embodiment of a step of removing the hard mask layer from theplanar waveguides and optionally from features in the optical device.

FIG. 26E. Embodiment of a step of forming an insulating layer.

FIG. 26F. Embodiment of a step of forming a patterned hard mask for theformation of cavities with z-pillars for the mounted die and forexposing the z-pillars for mounting and alignment of the fiber cablemounting block.

FIG. 26G. Embodiment of the step of forming cavities with z-pillars,cavities for the fiducials, and for exposing the z-pillars for mountingand alignment of the fiber cable mounting block.

FIG. 26H. Embodiment of the step of removing the hard mask afterformation of the cavities.

FIG. 26I. Perspective view of an embodiment of an interposer formed withz-pillar alignment aids in proximity to a v-groove shown with a portionof fiber optic cable placed in the v-groove but without the fibermounting block.

FIG. 26J. Perspective view of an embodiment of an interposer with aportion of fiber optic cable mounted in a fiber optic cable mountingblock and with fiber optic cable mounting block positioned on theinterposer with the core of the mounted fiber optic cable in alignmentwith a planar waveguide formed in the planar waveguide layer of theinterposer structure.

FIG. 26K. End view of a fiber optic cable mounting block on aninterposer with embodiments of z-pillar alignment aids: (i) z-pillarused for alignment in z-direction, and (ii) z-pillar configured foralignment in the z-direction and the lateral x-direction.

FIG. 27 . Embodiment of a method for forming and utilizing patternedalignment features on interposer substrate with mounted device and withfiber optic mounting block that includes an alignment aid used toposition the v-groove formed from the planar waveguide layer.

FIG. 28A. Embodiment of a step of forming an interposer substrate.

FIG. 28B. Embodiment of a step of forming a patterned hard mask for theformation of planar waveguides, fiducial marks, z-pillars, and lateralalignment aids for a fiber optic mounting block on an interposerstructure.

FIG. 28C. Embodiment of a step of patterning the planar waveguides,fiducial marks, z-pillars, and lateral alignment aids for a fiber opticmounting block on an interposer structure.

FIG. 28D. Embodiment of a step of removing the hard mask layer from theplanar waveguides and optionally from other features in the opticaldevice.

FIG. 28E. Embodiment of a step of forming an insulating layer.

FIG. 28F. Embodiment of a step of forming a patterned hard mask for theformation of a cavity with z-pillars and the fiber mounting blockalignment aids.

FIG. 28G. Embodiment of a step of forming cavities for the z-pillars,the fiducials, and for the fiber mounting block.

FIG. 28H. Embodiment of a step of removing the hard mask after formationof the cavities.

FIG. 28I. Embodiment of a step of forming a mask layer to facilitateformation of one or more optional v-grooves.

FIG. 28J. Embodiment of a step of removing the mask layer used tofacilitate formation of one or more optional v-grooves.

FIG. 28K. Perspective view of an embodiment of an interposer with amounted portion of fiber cable in a fiber mounting block.

FIG. 29A. Another embodiment of an interposer formed with z-pillars,fiducials and planar waveguides formed from a hard mask layer and thatincludes a combination of z-pillars and lateral alignment aids foralignment of the mounting block. The z-pillars and lateral alignmentaids are formed from the planar waveguide layer for alignment of thecore of a fiber optic cable mounted in the fiber optic cable mountingblock with waveguides or other optical devices formed on the interposer.

FIG. 29B. Embodiment of an interposer with z-pillars and alignment aidformed from the planar waveguide layer to support the alignment of afiber optic cable mounting block shown with the fiber optic cablemounting block.

FIG. 30A. Examples of fiber optic cable mounting blocks: (i) end viewwith a single fiber optic cable, (ii) end view with two fiber opticcables, and (iii) cross section along centerline of a portion of amounted fiber optic cable.

FIG. 30B. Another example of a fiber optic cable mounting block shown incross section through a single fiber optic cable. The core of the fiberis shown in alignment with a waveguide formed from the planar waveguidelayer of the interposer. Portions of z-pillar alignment structures arealso shown.

FIG. 30C. (i) Side view and (ii) Top-down view of an embodiment of afiber optic mounting block on an interposer. Top-down view showspositioning of the z-pillars adjacent to fiber optic cable.

FIG. 30D. Top-down view of an embodiment of an interposer thataccommodates a fiber optic mounting block with four fiber optic cables.The positioning of the alignment z-pillars in the embodiment is shownbetween the fiber optic cables mounted on the substrate.

DETAILED DESCRIPTION

Various embodiments are described herein with reference to theaccompanying drawings that are intended to convey the scope of theinvention to those skilled in the art. Accordingly, features andcomponents described in the examples of embodiments described herein maybe combined with features and components of other embodiments. Thepresent invention is not limited to the relative sizes and spacingsillustrated in the accompanying figures. It should be understood that a“layer” as referenced herein may include a single material layer or aplurality of layers. For example, an “insulating layer” may include asingle layer of a specific dielectric material such as silicon dioxide,or may include a plurality of layers such as one or more layers ofsilicon dioxide and one or more other layers such as silicon nitride,aluminum nitride, among others. The term “insulating layer” in thisexample, refers to the functional characteristic layer provided for thepurpose of providing the insulation property, and is not limited as suchto a single layer of a specific material. Similarly, an electricalinterconnect layer, as used herein, refers to a composite layer thatincludes both the electrically conductive materials for transmittingelectrical signals and the intermetal and other layers required toinsulate the electrically conductive materials. An electricalinterconnect layer, as described herein may therefore include apatterned layer of electrically conducting material such as copper oraluminum as well as the intermetal dielectric material such as silicondioxide, and spacer layers above and below the electrically conductivematerials, for example, among other layers. Additionally, referencesherein to a layer formed “on” a substrate or other layer may refer tothe layer formed directly on the substrate or other layer or on anintervening layer or layers formed on the substrate or other layer.References to the term “optical” devices, as used herein, may refer to apurely optical device such as a waveguide that does not have anelectrical feature and to an optoelectrical device that has both anoptical feature and an electrical feature, unless specified otherwise.An optical device, as used herein, is a device such as a waveguide, anarrayed waveguide, a spot size converter, a lens, a grating, amongothers, and an optoelectrical device is a device such as a laser or aphotodetector that includes an optical feature and an electricalfeature. In embodiments described herein, the use of the term “opticaldevice” may include both optical devices and optoelectrical devicesparticularly in the context of the alignment of optical features ofoptical die that pertains to devices with or without an electricalfeature. Like numbers in drawings refer to like elements throughout, andthe various layers and regions illustrated in the figures areillustrated schematically.

Embodiments of structures and methodologies are described herein for theformation and utilization of mechanical alignment aids that facilitatethe alignment of the optical planes of optical and optoelectricaldevices that are combined to form photonic integrated circuits (PICs)and the like. The alignment of the optical planes in these devices isrequired to facilitate the transference of optical signals between thedevices in the PICs.

Alignment features are described in embodiments, herein, that includemechanical alignment aids formed on a substrate of a first optical oroptoelectrical device and on a mating device to vertically align acommon optical plane between two optical devices. Mechanical alignmentaids, as described herein, include vertical alignment pillars,fiducials, lateral constraints, and other alignment aids that are formedon a substrate to facilitate the alignment of the optical pathways oftwo or more optical devices. Alignment of the optical pathways, ingeneral, is required in PICs to facilitate the transfer of opticalsignals between devices in an optical circuit.

In an embodiment, a z-pillar is formed on a first optical oroptoelectrical device and brought into contact with a mechanicalreference surface that is formed on a second optical or optoelectricaldie to form and align a common horizontal optical signal plane betweenthe two optical devices. As used herein, the term “z-pillar” is used todescribe a structural pillar formed on a substrate or device that isused to establish a reference in the “z” direction, normal to the flatsurface plane of the substrate or device as described and referencedherein. The reference height established by a z-pillar, in someembodiments, is the top surface of the z-pillar.

In some embodiments, a fiducial alignment feature is formed on a firstoptical or optoelectrical device and used to establish a lateralalignment reference to facilitate the placement or alignment of a secondoptical device that is brought into proximity with the first opticaldevice. The lateral alignment reference provided by the fiducial featureenables the alignment of a common lateral reference plane for the firstand second optical or optoelectrical devices to further enable theefficient transfer of optical signals between the two devices. As usedherein, a lateral reference is used to describe a reference formed on asubstrate or device that is used to establish a location or relativeposition in the “x” or “y” directions, perpendicular to the flat surfaceplane of the substrate or device. Lateral positioning using fiducials isnecessary for the placement of devices, for example, particularly inapplications that utilize automated die placement.

In other embodiments, one or more z-pillar alignment features arecombined with one or more lateral fiducial features to form alignmentreferences in both the vertical and the lateral directions for twooptical or optoelectrical devices for which the vertical and lateraloptical planes are brought into alignment to enable the efficienttransfer of optical signals between the two aligned devices. And in yetother embodiments, the one or more z-pillar alignment features that arecombined with one or more lateral fiducial features are further combinedwith lateral constraints that are formed on one or both of the opticaldevices for which the vertical and lateral optical planes are broughtinto alignment to enable the transfer of optical signals between the twoaligned devices. The lateral constraints, in embodiments, restrict thelateral movement of the two combined optical or optoelectrical die andmaintain the lateral alignment of the optical pathways between the twodevices. These lateral constraints, in combination with the verticalalignment constraint that is provided by the one or more z-pillars,provide an effective structure for three-dimensional alignment of theoptical pathways between two or more optical devices.

In some embodiments, the intersecting horizontal and verticalpropagation planes of one or more optical pathways of a first opticaldevice are aligned with the intersecting horizontal and verticalpropagation planes of one or more optical pathways of a second opticaldevice using alignment aids described herein that include the z-pillars,fiducials, and lateral constraints and the first optical device is aninterposer that includes a planar waveguide layer and an optionalelectrical interconnect layer on a substrate. The first optical device,or interposer, in embodiments, further forms a substrate to which thesecond optical device is mounted or otherwise combined.

In some embodiments, the interposer includes a planar waveguide layer ona substrate. The planar waveguide layer in embodiments, is a layer thatincludes a waveguide core and one or more of a top cladding layer, abottom cladding layer, a top spacer layer, a bottom spacer layer, a topbuffer layer, and a bottom buffer layer, among other layers. The corelayer in some embodiments, is a single waveguide layer. In otherembodiments, the core layer is a layered structure of one or more layersthat together form the core layer. In some preferred embodiments, thevertical and horizontal planes of two or more optical or optoelectricaldevices that are aligned using one or more of the z-pillars, thefiducials, and the lateral constraints, coincide or substantiallycoincide with the core layer of the planar waveguide layer, with thecore layer the preferred propagation path for optical signals within theplanar waveguide layer on the interposer.

In embodiments, the first optical device or interposer that includes aplanar waveguide layer from which optical waveguides are formed, furtherincludes an electrical interconnect layer that facilitates thetransmission of electrical signals between one or more electrical andoptoelectrical devices formed within, mounted to, or otherwise combinedwith the interposer. In some preferred embodiments in which the firstoptical device is an interposer, a common hard mask and lithographicprocess is used to pattern the waveguides, the z-pillars, the fiducials,and the lateral constraints. The use of a patterned hard mask andlithographic process, in embodiments, provides a common focal plane forthe planar waveguides and for the alignment aids, namely, the z-pillars,the fiducials, and the lateral constraints. In embodiments for which thefirst device is an interposer, the use of a common focal plane providesa reference plane on the interposer that is used in these embodiments tofacilitate the alignment of the optical features of two or more opticalor optoelectrical devices or die.

In yet other embodiments, the z-pillars, fiducials, and lateralconstraints further formed and integrated as described herein, providealignment aids that further facilitate the mounting and alignment of oneor more optoelectrical die onto the interposer to form all or a portionof a PIC. In some embodiments, in mounting a second optical oroptoelectrical device onto a first optical or optoelectrical device thatis an interposer, fiducials are used to facilitate the placement of thesecond optical or optoelectrical die onto the interposer, the topsurface of one or more z-pillars on the interposer are used to contact areference surface on the second die to establish its vertical positionon the interposer and to align the optical signal pathways in thevertical direction, and the lateral constraints, in combination with oneor more of the vertical surfaces of the z-pillars or other lateralalignment aids, are used to facilitate the lateral alignment of theoptical pathways and to provide mechanical stops for these mounted diewhen brought into their final positioning within the interposer. Theselateral constraints, in combination with the vertical alignment providedby the one or more z-pillars, provide a structure and method forthree-dimensional alignment between two or more optical devices usingthe interposer structure and methodology described herein.

In embodiments, a common lithographic patterning step and hard mask areused to pattern the fiducials and the z-pillars, and in some embodimentsto pattern the fiducials, the z-pillars, and the lateral constraints, toform a common focal plane on the interposer for these mechanicalalignment aids. In yet other embodiments, a common lithographicpatterning step and hard mask are used to pattern devices such aswaveguides, fiducials and the z-pillars, and in some embodiments topattern devices such as waveguides, the fiducials, the z-pillars, andthe lateral constraints, to form a common focal plane on the interposerfor these mechanical alignment aids.

In addition to the mechanical alignment aids that are formed on theinterposer, complementary alignment structures are also formed, inembodiments, on the second optical device that includes a verticalreference plane that contacts the top or another horizontal surface ofthe z-pillars of the interposer. Complementary mechanical alignmentstructures are additionally formed, in embodiments, to mate with thelateral constraints on the interposer. In an embodiment, for example,one or more triangular-shaped z-pillars are formed on the interposer andpositioned such that one or more complementary shaped triangularcavities on the second optoelectrical die, that when mounted on theinterposer, restrict and guide the lateral movement of the second die asit is placed and moved into a position of alignment as functionallyrequired by the PIC.

In embodiments, an interposer structure is formed that includes a planarwaveguide layer and an electrical interconnect layer on a substrate. Theplanar waveguide layer is formed on the electrical interconnect layer ofthe interposer structure and patterned using a first hard mask, such asaluminum. The first hard mask is used, in these and other embodiments,to pattern the planar waveguide layer to form one or more planarwaveguides, one or more fiducials, and one or more alignment referencepillars. The alignment reference pillars, as used herein, refer toalignment structures or reference structures that pertain to, contributeto, or somehow enable positioning or alignment of devices or features onthe interposer. The alignment reference pillars, in embodiments, providefor or contribute to the alignment of structures or features of theinterposer and the optoelectrical die that are integrated or coupled insome way with the interposers. These alignment reference pillars canprovide for, or contribute to, the alignment of features in the verticaldirection (z-reference), in one or more lateral directions (x-yreference), or both the vertical and one or more lateral directions.Concurrent lithographic patterning of the planar waveguides, thefiducial marks, and the alignment reference pillars on the interposerstructure enables the precise lateral positioning of these features inrelation to other features on the interposer, and provides practicaladvantages in the processing steps subsequent to this patterning step.The precise positioning of the alignment fiducials relative to thealignment reference pillars and the patterned planar waveguides,provides the capability for accurate placement of pre-fabricatedoptoelectrical and optical die onto the interposer when using thefiducials as a placement reference. In general, the accuracy provided bythe lithographic patterning process is quite high, and the use of thistechnique to pattern the hard mask that is used to define the planarwaveguides, the fiducials, and the alignment reference pillars ensuresthat these structures are fabricated with the high degree of accuracythat is provided by the concurrent lithographic patterning of thesestructures.

In embodiments, the patterned alignment reference pillars are formed ina portion of the interposer within which the optoelectrical and opticaldie are typically mounted, and provide a reference height to enable thevertical alignment of features of the mounted optoelectrical and opticaldie with features of the interposer substrate. Precise alignment oflaser facets, for example, with the planar waveguides on the interposeris imperative for efficient operation of the PICs formed on theinterposer with integrated laser die. In addition to the accuratelateral positioning of the alignment reference pillars formed on theinterposer, vertical alignment is also provided in embodiments, to ahigh degree of accuracy relative to the planar waveguides, since thesepillars are formed using the same hard mask at the same vertical heightas the planar waveguide of the interposer.

In embodiments, the first hard mask is removed from the patternedwaveguides after the planar waveguide layer has been etched, but remainson the fiducial marks and the partially-formed alignment referencepillar features. One or more electrically insulating layers that caninclude one or more of a spacer layer, a buffer layer, and planarizationlayer, among others, are formed over the patterned waveguides, thefiducial marks, and the z-reference pillar structures. Coverage of thehard mask patterned, partially-formed pillar structures with theinsulating layer results in the formation of buried, partially formedpillar structures that remain patterned with the first hard mask,although buried within the thick insulating structure. In embodiments, asecond hard mask is formed over the thick deposited insulating structureto protect the unmasked planar waveguides and allow for the formation ofrecesses in the interposer structure within which the optoelectrical oroptical die are to be mounted. Removal of the hard mask from the planarwaveguides formed from the planar waveguide layer and subsequentcoverage of the unmasked waveguides with cladding is necessary foroptimal propagation of the optical signals through the waveguides. Thepatterned alignment reference pillars with the buried first hard masklie within the area of the die within which the recesses are formed. Inembodiments, the etching of the thick insulating layer, through openregions defined by the second hard mask, exposes the buriedhard-mask-patterned, reference pillars to this etch process and resultsin the re-exposure of the alignment reference pillars wherein thesereference features provide precise lateral positioning as a consequenceof having been exposed to the same lithographic patterning steps as theplanar waveguides and fiducials and precise vertical positioning as aconsequence of having been patterned using the same hard mask as theplanar waveguides and fiducials. Thus, precise alignment references areprovided, in embodiments, for both lateral and vertical positioning ofoptoelectrical die onto the interposer.

After formation of the recesses in the thick insulating layers on theinterposer, subsequent placement of the pre-formed optoelectrical dieinto the recesses can be achieved with reference to the buried fiducialsthat were formed concurrently with the planar waveguides and thealignment reference pillars. Vertical self-alignment of theoptoelectrical devices with the planar waveguides within the recessesformed in the interposer is achieved, in embodiments, as a result of thepositioning of the pre-formed die over the alignment pillars and thesubsequent use of the lateral positioning of the pillars to guide thedie into an aligned position. Alignment and positioning of thepre-formed die is further facilitated, in some embodiments, withmechanical alignment aids that are formed on these die.

In addition to the formation of an interposer structure with alignmentfeatures, in some embodiments, the structures and methodologies foralignment include the formation and implementation of mechanicalalignment features on both the interposers and on the optoelectrical andoptical die that are integrated within the interposers. The integrationof pre-formed optoelectrical and optical die into interposers, inembodiments, benefits from the inclusion of mechanical alignmentfeatures and the associated protocols that enable the utilization ofthese mechanical alignment features to achieve improved operationalperformance. In embodiments, mechanical alignment features include theuse of mechanical stops that are formed both on interposer substrate incombination with complementary-shaped mechanical stops that are formedon optoelectrical or optical die that are compatible with the alignmentstructure on the interposer substrates. These complementary mechanicalalignment features, in embodiments, are particularly beneficial forproviding alignment within the lateral plane of the substrate, hereinreferred to and referenced as alignment in the “x” and “y” directions.In some embodiments, the lateral x and y alignment features on theinterposer are formed by lithographic patterning and subsequent etchingof the alignment reference pillars to form nestable shapes in thelateral plane. Compatibly shaped features that are formed on theoptoelectrical and optical die enable the alignment of these mechanicalalignment features on the die with the nestable features on theinterposer to align the die to the interposer.

Features of optoelectrical die that require alignment with matingfeatures on the interposer can include, for example, emitting facets ofan optoelectrical device such as a laser or LED, or a portion of aphotodiode that receives an optical signal for detection. These featuresof optoelectrical die can be aligned, for example, with features on theinterposer that can include planar waveguides and other optical devicesformed on the interposer.

In an embodiment, mechanical alignment aids are formed on an interposerin the form of triangularly-shaped pillars as viewed from a top-downperspective of the interposer. A reference height for these triangularpillars is established by the hard mask layer that is used to patternthese triangular pillars concurrently with one or more planar waveguidesand one or more fiducials. A reference height is also provided, asdescribed herein in embodiments, on compatible optoelectrical or opticaldie. Complementary-shaped triangular cavities that are designed tolaterally guide the movement of the optoelectrical or optical die areformed on the optoelectrical or optical die and enable the alignment ofoptoelectrical, optical, or electrical features on the die with opticalor other features on the interposer. In these embodiments, during anassembly process, the triangular-shaped cavity features on theoptoelectrical or optical die are firstly placed over the triangularpillars of the interposer, and secondly, once placed, the compatiblyshaped features on the interposer and the die allow for theoptoelectrical die to be guided into place on the interposer. As thetriangular features are brought into alignment in these embodiments, theoptical facets or other features of the optoelectrical or optical dieare brought into lateral alignment with the optoelectrical or opticalfacets or other features on the interposer. The vertical alignment ofthese features is established, in embodiments, with a vertical referencestop on the optoelectrical or optical die that is brought into contactwith the top of the alignment reference pillars. In addition to theoptical features that are brought into alignment in these embodiments,electrical contacts between the interposer and the mating optoelectricaldie can also be brought into alignment or used to facilitate thealignment process. Intentionally misaligned solder connections atplacement, as encountered for example in some embodiments, are used toexert a force on the optoelectrical die upon the application of a heatsource. The exerted force on the placed die upon heating will act tomove the misaligned solder connections into alignment and the alignmentfeatures will guide the moving die into a preferred lateral alignmentposition on the interposer.

In other embodiments, non-triangular-shaped pillars are formed on aninterposer, and complementarily-shaped cavity features are formed onoptoelectrical or optical die that facilitate the positioning of thesedie to the interposer and that further facilitate and enable thealignment of optoelectrical, optical, and electrical features on the diewith features on the interposer. In these embodiments, alignment pillarsthat are semi-circular, trapezoidal, hexagonal, or any shape orcombination of shapes are formed on the interposer andcomplementary-shaped cavity features are formed on the optoelectrical oroptical die that allow for the alignment of the features formed on thesedie with the alignment reference pillars formed on the interposer.

In other embodiments, one or more alignment reference pillars are formedon the interposer with one or more complementarily shaped structureformed on the optoelectrical or optical die that are to be aligned withthe interposer. In some embodiments, more than one alignment pillar isformed on an interposer and the alignment pillars are the same orsimilar in shape. In other embodiments, more than one alignment pillaris formed on the interposer and the alignment pillars are not the sameshape. In these and other embodiments, complementary-shaped structuresare formed on the optoelectrical or optical die that are aligned withthe alignment pillars on the interposer.

In some embodiments, a combination of alignment reference pillars isformed on the interposer that provide both a guide for movement intoalignment and a hard stop for limiting the overall movement of the dierelative to the interposer. And in yet other embodiments, a combinationof pillars and complementary-shaped cavity structures are formed on theinterposer, and a combination of compatibly-shaped pillars andcomplementary-shaped cavity structures are formed on the optoelectricalor optical die. And in yet other embodiments, one or more pillars areformed on the optoelectrical die with one or more compatibly shapedcavity features formed on the interposer, and one or more pillars areformed on the interposer with one or more compatibly shaped cavityfeatures on the optoelectrical or optical die.

In addition to the features described in embodiments for aligningoptical devices that include optical and optoelectrical devices oninterposer-based substrates, alignment structures and methods aredescribed in which v-grooves are formed in alignment with planarwaveguides formed from the planar waveguide layer of the interposer andin which fiber optic cable mounting blocks are aligned and mounted tothe interposer substrates. Other alignment configurations and structuresare also described. Alignment aids that include lateral constraints andlithographic patterning aids that are formed from planar waveguidelayers are also described herein.

The alignment of optical or electrical features of an optoelectrical diewith optical or electrical features on an interposer is enabled with theformation of complementary-shaped alignment structures on both theinterposers and on the optoelectrical and optical die that are mountedto these interposers. The implementation and utilization of thesealignment structures enables the alignment of interposer substrates andthe die that are integrated with these interposers for the purpose offorming the interposer-based PICs. Simplifications in alignmentstructures and procedures, in embodiments described herein, allow forpassive alignment processes that are economically beneficial overtechniques that require active or interactive alignment processes.Additionally, the simplified alignment structures and associatedprocesses can provide further benefit by reducing the optical orelectrical losses that result from misaligned or inadequately aligneddevices in photonic integrated circuits that utilize these structures.Thusly, the techniques described herein offer technical advantages andeconomic advantages in the alignment of optical and electrical featuresof mounted optoelectrical and optical die and the interposers orsubstrates to which these dice are attached.

In FIG. 1(i), a schematic drawing of two optical or optoelectricaldevices is shown with common horizontal optical signal plane 107 andcommon vertical signal plane 108. Referencing the orthogonal coordinatesystem shown in FIG. 1(i), a horizontal signal plane 107, as describedherein, is a geometrical plane parallel to the x-y plane. The verticalposition of the horizontal signal plane is determined by its heightalong the z-axis of the reference coordinate system. Again referencingthe orthogonal coordinate system shown in FIG. 1(i), a vertical signalplane 108, as described herein, is a geometrical plane that can beparallel to the reference x-z plane or to the reference y-z plane. Thex-z and y-z planes, and the planes parallel to these planes are alsoreferenced herein as the lateral alignment planes. FIG. 1(i) shows thevertical signal planes 108 of two optical or optoelectrical devices tobe in alignment along the x-axis. Two optical devices are said to be inalignment, as referenced herein, when the horizontal signal plane 107and the vertical signal plane 108 are in alignment. Devices 112, 122 areoptical or optoelectrical devices that include an optical element to orfrom which an optical signal can be emitted by, received by, orpropagated through and include emissive devices such as lasers and LEDs,receiving devices such as photodetectors, and passive devices such aswaveguides, among many others. Devices 112, 122 are devices, forexample, that are used in the formation of photonic integrated circuits(PICs) and may be optical devices such as a waveguide, an arrayedwaveguide, a grating, among others, or may be an optoelectrical devicesuch as a laser or photodiode, among other devices, that have both anoptical and an electrical feature. In PICs, devices 112, 122 benefitfrom accurate placement and alignment of the optical features inapplications in which efficient optical signal transfer providesimproved operation of the PICs that are fabricated from these devices.The effectiveness of an alignment method on the alignment of the opticalor optoelectrical devices 112, 120 can be measured, for example, by theloss in signal power or intensity as an optical signal is transferred orotherwise communicated from one to another device in the PIC. Andalthough the effectiveness of the alignment of devices 112, 120 isultimately measured by the efficiency in the power or signal transferbetween devices 112, 120, the use of a power measurement duringfabrication of the PICs can require an active alignment method in whichthe power or optical signal strength is measured during the alignmentprocess to ascertain the optimal positions for peak signal transfer.More preferably, passive techniques and the associated structures usedin these methods allow for effective alignment of the optical devices ina PIC without the need for acquiring active measurements and feedback inthe alignment process.

An optical device, as referenced herein, is a device that has an opticalfeature that sends, receives, reflects, transmits, focuses, alters,amplifies, or somehow influences the formation, transmission,propagation, detection, or transfer, or any property of an opticalsignal. An optoelectrical device, as referenced herein, is a form ofoptical device with an electrical feature. The electrical feature can beintegral to the optoelectrical device or can be a portion of anoptoelectrical device that is coupled to one or more otheroptoelectrical devices to send, receive, reflect, transmit, focus,alter, amplify, or somehow influences the formation, transmission,propagation, detection, or transfer, or any property of an opticalsignal. Optoelectrical devices such as lasers are used, for example, toform an optical signal from an electrical signal applied to the lasingdevice. Photodetectors, are used, for example, to convert an opticalsignal to an electrical signal. These and many other forms of opticaland optoelectrical devices can be used in the formation of photonicintegrated circuits that benefit from structures and methods that ensurethe devices are properly aligned as required by the design andfunctionality of the circuit. The term “optical devices” as used herein,is intended to include optoelectrical devices, as the alignmenttechniques described herein pertain to the optical axes and features ofeither optical or optoelectrical devices.

Referring to FIG. 1 (ii), optical devices 112, 120 are shown positionedon substrate 100. FIG. 1 (ii) shows a first optical or optoelectricaldevice 112 with horizontal optical signal plane 107 a in alignment withthe horizontal optical signal plane 107 b of a second optical device120. The alignment of the horizontal signal planes is hereinafterreferred to as alignment in the “z” direction as indicated by thereference coordinate frames in FIG. 1 (ii). Alignment in the “z”direction can be in the “+z” or “−z” direction and can be influenced,for example, by the vertical position of the optical devices on thesubstrate or a feature on the substrate upon which the devices 112, 120are mounted, and by the position of the optical signal plane within theoptical devices. An aspect of embodiments is to provide structures andmethods for aligning the horizontal optical signal planes 107 a, 107 bof two or more devices 112, 120.

Referring again to FIG. 1 (ii), a first optical device 112 is shown withvertical optical signal plane 108 a in alignment with the horizontaloptical signal plane 108 b of a second optical device 120. In general,the alignment of the vertical optical signal planes such as verticaloptical signal planes 108 a, 108 b can be made in reference to anylateral plane, but for the purposes of discussion herein, specificreference planes are identified to facilitate illustration of thefeatures of embodiments. Accordingly, the alignment of the verticaloptical signal planes 108 a, 108 b in the horizontal direction as shownin FIG. 1 (ii) is hereinafter referred to as alignment in the “x”direction as indicated by the reference coordinate frames in FIG. 1(ii). Alignment in the “x” direction can be in the “+x” or “−x”direction and can be influenced, for example, by the horizontalplacement of the optical devices on the substrate or a feature on thesubstrate upon which the devices 112, 120 are mounted and by theposition of the optical plane within the optical devices. Another aspectof embodiments is to provide structures and methods for aligning thehorizontal optical planes 108 a, 108 b of two or more devices 112, 120.

Referring again to FIG. 1 (ii), a first optical or optoelectrical device112 is shown with optical signal planes 107 a, 108 a in alignment withthe optical signal planes 107 b, 108 b of a second optical oroptoelectrical device 120. The spacing between the optical devices 112,120 or features of these optical devices 112, 120 in the horizontaldirection shown in FIG. 1 (ii) is hereinafter referred to as alignmentin the “y” direction as indicated by the reference coordinate frames inFIG. 1 (ii). Alignment in the “y” direction can be in the “+y” or “−y”direction and can be influenced, for example, by the horizontalplacement and position of the optical devices on the substrate or afeature on the substrate upon which the devices 112, 120 are mounted.Yet another aspect of embodiments is to provide structures and methodsfor accurately spacing the optical devices 112, 120 or features of theoptical devices 112, 120.

Fabrication methods and structures are disclosed herein that providepassive alignment of optical features of paired optical devices 112,120. These fabrication techniques also provide for the precise placementof, and spacing between, the devices and more specifically the opticalfacets of these devices.

Referring to FIG. 2(i), a first optical device 212 is shown in crosssection with the vertical optical signal plane 207 a and second opticaldevice 220 with corresponding vertical optical signal plane 207 b. FIG.2(i) shows the two optical devices 212, 220 with the vertical componentsof the optical signal planes 207 a, 207 b in alignment along thez-direction of the reference coordinate system. Also shown in FIG. 2(i)is reference plane 225ref. Reference plane 225ref may be, for example,the top surface of a substrate, the top of one or more features formedon a substrate, or other reference plane formed from, or in referenceto, a feature on the substrate or device mounted on the substrate.

Referring to FIG. 2 (ii), a schematic cross-sectional view of verticallyaligned optical devices 212, 220 is shown with these devices mounted onsubstrate 200 with reference plane 225ref to form all or part of a PIC202. In FIG. 2(u), reference plane 225ref refers to the surface of thesubstrate 200 and the vertical signal plane 207 of the PIC 202 is shownat a height “z” along the vertical axis from the reference plane 225ref.The conventions and elements shown in FIG. 2 are used to describesimilar features and elements in embodiments described herein.

Referring to FIG. 3(i), a schematic cross-sectional view of anembodiment that includes vertically aligned optical devices 312, 320 isshown. In this embodiment, optical device 312 is formed from substrate300 and includes an optical feature with optical axis 307 a. Opticaldevice 312 shown in FIG. 3(i) is, for example, an optical waveguide,formed within or on substrate 300. The fixed optical axis 307 a of theoptical device 312 is shown in FIG. 3(i) in alignment with the opticalaxis 307 b of the mounted optical device 320. In this embodiment, thevertical positioning of the optical axis 307 b of device 320 isdetermined by the height of pillar 334 upon which the device 320 ismounted, by the vertical position of the 326ref plane of device 320, andby the spacing between the reference plane 326ref and the optical axis307 b of the optical device 320. Pillar 334, hereinafter referred to asa z-pillar, is formed in cavity 348 within substrate 300. A referenceplane 325ref is shown in FIG. 3(i) that corresponds to the top of thez-pillar 334 and, in the embodiment shown in FIG. 3(i), this referenceplane also corresponds to the optical axis 307 of PIC 302. In thisembodiment, no offset is present between the optical axis 307 and thevertical reference plane 325ref that corresponds to the top of thez-pillar. Additionally, in this embodiment, no offset is present betweenthe reference plane 326ref of the device 320 and the optical axis 307 bof the optical device 320. In other embodiments, as presented herein,these reference planes need not be in alignment.

Referring to FIG. 3 (ii), a schematic cross-sectional view of anembodiment that includes vertically aligned optical devices 312, 320 isshown for which the 325ref plane at the top of the z-pillar 334 is notin alignment with the optical axis 307 of the PIC 302. In thisembodiment, the height of the z-pillar is shown to be higher than in theembodiment in FIG. 3(i) and this increased height of the z-pillar isrequired to compensate for the increased distance between the referenceplane 326ref and the optical axis 307 b of the device 320 in FIG. 3(u).In embodiments, masking layers that are used to pattern the z-pillarsmay remain in place after etching, for example, that lead to the offsetin the optical axes as shown. Differences in the distance betweenoptical axes 307 b and the mechanical reference plane 326ref may alsolead to an offset between the top surface of the z-pillar and theoptical axis 307 b of mounted optical devices such as optical device320.

Referring to FIG. 4 , an embodiment of an interposer structure is shown.FIG. 4(i) shows a schematic perspective drawing of an embodiment of aninterposer structure 404 that includes a planar waveguide layer 405 on abase structure 401. The base structure 401 includes an optionalelectrical interconnect layer 403 and a substrate 400. The interposerstructure 404 is used, for example, in full or in part in thefabrication of photonic integrated circuits. In embodiments, substrate400 is a semiconductor substrate such as a silicon substrate. In someembodiments, substrate 400 includes one or more layers of asemiconductor material such as silicon, indium phosphide, galliumarsenide, or another semiconductor. In other embodiments, a ceramic orinsulating substrate is used. In yet other embodiments, a metalsubstrate is used. And in yet other embodiments, a combination of one ormore semiconductor layers, insulating layers, and metal layers are usedto form a substrate 400 upon which the optional electrical interconnectlayer 403 and the planar waveguide layer 405 are formed. In someembodiments, the electrical interconnect layer 403 is not in directcontact with the substrate but rather an intervening layer is present.Similarly, the planar waveguide layer 405, in some embodiments, is notin direct contact with the underlying electrical interconnect layer 403but rather an intervening layer or layers may be present.

FIG. 4 (ii) shows a schematic cross section of embodiments of apatterned planar waveguide 444 formed from the planar waveguide layer405 in additional detail. The patterned planar waveguide 444 illustratedin FIG. 4 is a multilayer planar waveguide layer 405 that includes afirst dielectric layer 459, a second dielectric layer 458, and a thirddielectric layer 457. Each layer in this multilayer structure 405 caninclude one or more layers. The multilayer structure 405 is formed inthe embodiment shown, on the electrical interconnect layer 403. Inembodiments, the electrical interconnect layer 403 of the interposerstructure is formed on substrate 400 to form base structure 401. Thefirst dielectric layer 459 is one or more of a cladding layer, a spacerlayer, and a buffer layer, among other insulating and dielectric layers.The planar waveguide layer 405, in the embodiment shown in FIG. 4 , alsoincludes a second dielectric layer 458 on the first dielectric layer459. The second dielectric layer, in embodiments, is a core layer 458that forms the primary propagation path for the optical signal 970, forexample. The core layer 458, in some embodiments, is a single dielectriclayer such as silicon oxynitride, silicon nitride, or silicon dioxide.In other embodiments, the core layer 458 is a multilayered structurethat includes one or more layers of, for example, silicon oxynitride,silicon nitride, or silicon dioxide. The third dielectric layer 457includes one or more of a cladding layer, a spacer layer, and a bufferlayer, among other insulating and dielectric layers.

Planar waveguide layer 405 of FIG. 4 (ii) includes core layer 458. Thecore layer 458, in some embodiments, is a layer of dielectric materialor a semiconductor material through which optical signals can propagate.The core layer 458, in some embodiments, is a single layer, and in otherembodiments includes two or more layers. In some embodiments, the corelayer 458 is a superlattice structure that includes a stacked structureof multiple dielectric films. A bottom layer 459 of the planar waveguidelayer 405 in some embodiments, is a bottom cladding layer. In otherembodiments, the bottom layer 459 is one or more of a cladding layer, aspacer layer, and a buffer layer, among other layers. The bottom layer459 typically has a lower index of refraction than the core layer 458 toprovide containment of optical signals propagating in the waveguides.Spacer layers and buffers layers in the planar waveguide layer providean isolation function, from the substrate for example, and a spacingfunction, that enables the alignment of the core layer 458 to align withone or more elements in a PIC. Other embodiments may include otherlayers in the bottom layer 459. Similarly, a top layer 457 of the planarwaveguide layer 405 in some embodiments, is a top cladding layer. Inother embodiments, the top layer 457 is one or more of a cladding layer,a spacer layer, and a buffer layer, among other layers. The top layer457 typically has a lower index of refraction than the core layer 458.Spacer layers and buffers layers in the planar waveguide layer 405provide an isolation function, from the substrate for example, and aspacing function, that enables the alignment of the core layer 458 toalign with one or more elements in a PIC. Other embodiments may includeother layers in the top layer 457. The schematic drawing in FIG. 4 (ii)also shows a layer 438 that envelops the planar waveguide structure 405.Layer 438, in embodiments, is one or more of a passivation layer, anencapsulation layer, and a planarization layer, among others. Layer 438,for example, in embodiments, is a layer within which cavities orrecesses are provided to form receptacles for optical and optoelectricaldie that are mounted on the interposer 404 as further described herein.

In embodiments, planar waveguides layer 405 is patterned and formed intoplanar waveguides 444 and the core 458 of the patterned planar waveguide444, is aligned with the optical features of an optical oroptoelectrical device such that an optical signal is transmitted fromthe optical feature of the optical or optoelectrical device to the core458 of the planar waveguide 444 or conversely, is received by the core458 of the planar waveguide 444 from the optical feature of the opticalor optoelectrical device. In an embodiment, an optoelectrical devicesuch as a laser, for example, is used with the planar waveguide, and theemitting portion of the laser is substantially aligned with the core 458of the planar waveguide layer 405. In this embodiment, the alignment ofthe core 458 of the planar waveguide layer 405 with the emitting portionof the facet of the laser, enables an optical signal from the laser tobe received by the core 458 of the planar waveguide layer 405 forpropagation in the PIC within which the laser and the planar waveguideare included. In yet another example, for which the optoelectricaldevice is a photodetector, alignment of the core 458 of the planarwaveguide layer with the edge facet of the photodetector allows for anoptical signal from the planar waveguide core 458 to be substantiallyreceived by the photodetector. In these and other embodiments,additional devices can be included in the PIC such as lenses, spot sizeconverters, among many others, to facilitate the coupling of opticalsignals through the PIC. In embodiments described herein, two arbitrarydevices are often shown for reference but many devices may be includedin the circuit.

Referring to FIG. 4 (iii), a cross sectional schematic is shown of anembodiment of interposer 404 with additional detail provided for theoptional electrical interconnect layer 403. In the embodiments of theelectrical interconnect layer 403 of the interposer structure 404 shownin FIG. 4 (iii), conductive interconnects are formed from one or morelayers of lateral electrical connections 432 and vertical electricalconnections 433. Electrical interconnections 432,433 are encapsulated inthe embodiment shown in FIG. 4 (iii) in intermetal dielectric 439. Inembodiments, device 420 is mounted to the interposer 404 in a cavity 448formed in insulating layer 438 and through planar waveguide layer 405.Device 420 is shown, in embodiments, with optical axis in opticalalignment with the core of the planar waveguide layer 405. Inembodiments, the electrical interconnect layer 403 of the interposer 404provides electrical interconnectivity between one or more optoelectricaldevices mounted on the interposer 404, and to electrical contact pads toprovide interconnectivity to sub-mounts and external devices, forexample. Optionally, in some embodiments, one or more buried electricaldevices 435 can also be interconnected with the interconnects in theelectrical interconnect layer 403.

Referring to FIGS. 5A-5C, embodiments of a number of alignment aids aredescribed that are formed in embodiments in the interposer 404 of FIG. 4in an integrated manner that facilitates alignment of the optical axesof optical devices and device structures formed on an interposerstructure. The alignment aids described in FIG. 5 include a fiducial, az-pillar, and a lateral constraint. In FIG. 5A, a fiducial mark 514 isshown that is used in embodiments to facilitate the lateral positioningof devices and device features on a substrate. Automated positioning andplacement apparatus is commonly used to position die for mounting onto asubstrate using a fiducial marking for reference before positioning ofthe die onto the mounting assembly. In FIG. 5B, a z-pillar alignment aidis described that is used in embodiments to facilitate the verticalpositioning of devices and device features on a substrate. And in FIG.5C, a lateral constraint alignment aids are described that are used inembodiments to facilitate a combination of lateral and verticalpositioning of devices and device features on a substrate. Thestructures and methods of formation of these structures are presentedherein.

In FIG. 5A, fiducial mark 514 is shown in the top down view and thesection A-A′ view with two aligned optical devices that include a firstoptical device 512, namely a planar waveguide formed on an interposer,and a second optical device, namely a discrete optical device 520 thatis mounted onto the optical interposer device 512 in cavity 548.Fiducial mark 514 is shown formed in a cavity 549, the formation ofwhich allows for improved visibility of the fiducial 514. The improvedvisibility of the fiducial 514 with the formation of the cavity 549provides improved resolution for lateral positioning devices andequipment that are used in the placement of the devices 520 into thecavity 548. Improved resolution is achievable with the capability toachieve optical focus on the exposed fiducial that may not be achievablein structures for which fiducials are buried within other layers and notoptically visible. Additionally, fiducials formed at or near the samehorizontal plane as the optical axes of devices provide a higher degreeof positioning accuracy than fiducials formed at other locations furtherabove, or below, the optical alignment axes. The fiducial 514 is analignment aid, and in the embodiment shown in FIG. 5A, the fiducial mark514 provides a reference position in the lateral directions, namely, thex and y directions, as shown in the reference coordinate system in thetop-down view of FIG. 5A. In embodiments, the reference positionestablished by any portion of the fiducial is typically, but notnecessarily, laterally offset in one or both the x and y directionsrelative to the position of the optical signal plane 508 and the lateraloptical reference planes 508 a, 508 b of the devices 512, 520. Thelateral reference position provided by the fiducial 514, in embodiments,provides a means for accurately placing the optical device 520 intocavity 548 of the optical device 512, and further provides a means foraligning the optical planes 508 a, 508 b of the two devices 512, 520.Referring to the Top Down View of FIG. 5A, device 520 is positioned ontothe device 512 with an offset in the x-direction and in the y-directionrelative to the fiducial 514. Placement of devices onto interposers anddevice submounts using automated placement equipment is well understoodin the art of semiconductor device manufacturing. The top down view inFIG. 5A shows the alignment of the vertical planes of the optical signalaxes 508 a, 508 b of the optical devices 512, 520, respectively, afterplacement of the device 520. Referring to the Section A-A′ drawing ofFIG. 5A, the fiducial 514 is shown in substantial alignment with thehorizontal optical axis 507 of the PIC 502. Also shown in alignment arethe horizontal components of the optical signal axes 507 a, 507 b of theoptical devices 512, 520. PIC 502 includes the optical devices 512, 520and may include additional optical and optoelectrical devices,electrical devices, and other circuit elements. The fiducial is one of anumber of alignment aids that are formed in embodiments that aredescribed in conjunction with additional alignment aids furtherdescribed herein. The fiducial reference is generally an edge referenceand as such, the thickness of the hard mask layer will not directlyaffect the accuracy of the positioning using the fiducial when the edgesof the hard mask in close vertical alignment with the layer within whichthe optical axes reside. If the hard mask has a severely tapered profileat the edge, this taper can affect the resolution of the positioningaccuracy when using the fiducial for positioning.

Referring to FIG. 5B, a z-pillar alignment aid is introduced anddescribed. In FIG. 5B, a schematic top down view and cross section view(Section B-B′) are shown to illustrate an embodiment in which a z-pillaralignment aid is used in the alignment of two optical devices 512, 520.The aligned horizontal optical planes 507 a, 507 b, respectively, ofdevices 512, 520 are shown in optical alignment as facilitated by thez-pillar mechanical alignment aid 534 that is formed in a cavity 548 ondevice 512. Device 512 in the embodiment shown in FIG. 5B is an opticalwaveguide formed in the interposer substrate 500. Mechanical alignmentaid 534 shown in FIG. 5B is a vertical alignment pillar. In theembodiment shown in FIG. 5B, the top surface of the vertical alignmentpillar, or z-reference pillar as described herein, provides a referenceheight and contact surface upon which a device such as optical device520 is mounted to provide for alignment of the optical features of atleast two devices in at least the vertical direction. In someembodiments, the reference height established by the top surface of thez-pillar 534 has a vertical offset (shown as “z-offset” in Section A-A′of FIG. 5B) from the optical reference planes 507 a, 507 b of thedevices 512, 520. FIG. 5B shows an embodiment with such an offset. Inother embodiments, the reference height established by the top surfaceof the z-pillar 534 is aligned with the optical reference planes 507 a,507 b of the devices 512, 520. The bottom surface of the device 520,with vertical reference plane 526ref, forms a surface-to-surface contactwith the top surface of the z-pillar 534, which coincides with thehorizontal reference plane 525ref of device 512. This surface-to-surfacecontact provides for the precise alignment of the optical signal planes507 a, 507 b between the two devices 512, 520, respectively. Inembodiments in which a z-offset is present between the top surface ofthe z-pillar 534 on device 512 and the optical plane 507 a of the PIC502, a similar z-offset is also provided on the device 520 between theoptical plane 507 b and the top surface of the z-pillar 534 at thereference plane 525ref. In the top-down view of the embodiment of thealignment aids of the PIC 502 shown in FIG. 5B, a single z-pillar isshown for illustration purposes. Embodiments with more than one z-pillarare described further herein and within the scope of embodiments. Thetop-down view shows fiducial alignment aid 514 in cavity 549 withoffsets to the lateral alignment planes 508 a, 508 b to facilitate theplacement of device 520 into cavity 548 and subsequent alignment of theoptical axes 508 a, 508 b of the devices 512, 520.

Referring to FIG. 5C, a lateral constraint alignment aid is introducedand described. In FIG. 5C, schematic top down view and a cross sectionalview (Section C-C′) are shown to illustrate an embodiment in which alateral constraint is used to facilitate the alignment of two optical oroptoelectrical devices 512, 520. In the embodiment, the horizontaloptical planes 507 a, 507 b and vertical optical planes 508 a, 508 b,respectively, are shown in alignment as facilitated by a lateralconstraint alignment aid formed in the interposer in combination withthe fiducial and z-pillar alignment aids. In the embodiment, a z-pillarmechanical alignment aid 534 that is formed in cavity 548 and a fiducialalignment aid 514 that is formed in a cavity 549 are shown with alateral constraint alignment aid 581. In the embodiment shown in FIG.5C, the lateral constraint 581 results from the surface contact that isformed between the sidewall of the z-pillar 534 of the device 512 andthe mechanical feature 580 of the device 520. Alignment aid 514 shown inFIG. 5C, namely the fiducial mark, provides a lateral reference positionin the x and y directions as shown in the reference coordinate system inthe top-down view of FIG. 5C. Furthermore, the fiducial 514 is formed inthe same horizontal plane as the z-pillar 534 in the embodiment shown.In embodiments, the reference position established by any portion of thefiducial 514 typically, although not necessarily, is laterally offset inone or both the x and y directions relative to the position of thehorizontal optical signal plane 508 and the lateral optical referenceplanes 508 a, 508 b of the devices 512, 520. The lateral referenceposition provided by the fiducial 514, in embodiments, provides a meansfor accurately placing the second optical device 520 into cavity 548 ofthe first optical device 512, and further provides a means for aligningthe horizontal optical planes 508 a, 508 b of the two devices 512, 520.In the embodiment shown in FIG. 5C, the top surface of the z-pillar 534provides a contact surface that contacts a reference surface 526ref onthe device 520 upon placement into the cavity 548 to establish theheight of the optical plane of the device 520. In some embodiments, thereference height established by the top surface of the z-pillar 534 hasa vertical offset (shown as “z-offset” in Section A-A′ of FIG. 5C) fromthe optical reference planes 507 a, 507 b of the devices 512, 520 as isthe case for the embodiment shown in FIG. 5C. A similar z-offset to thatprovided by the z-pillar is provided in the device 520 to offset thereference surface 526ref from the optical plane 507 b to enable thealignment of the two optical planes 507 a, 507 b of the two devices 512,520, respectively. In other embodiments, the reference heightestablished by the top surface of the z-pillar is aligned with theoptical reference planes 507 a, 507 b of the devices 512, 520 althoughthese embodiments are not shown in FIG. 5C. Mechanical aid 534 furtherforms a portion of a lateral constraint 581 that limits the movement ofthe optical device in the lateral y-direction as indicated by thereference coordinates shown in FIG. 5C. In embodiments, the device 520is placed in the recess 548 of the first device 512, and the placementof the device is such that the mounted device 520 does not make contactwith the sidewalls of the recess 548 of the first device 512 withinwhich device 520 is placed. To prevent contact with the sidewalls of therecess 548, the device 520 is placed with adequate clearance with thesidewalls of the recess 548 and then moved into position afterplacement. The lateral constraint alignment aids 581 limit the movementof the second device 520 in at least one of the lateral directions,namely the x and y directions. In the embodiment shown in FIG. 5C, thelateral constraint alignment aids 581 as shown limit the movement inboth the x and y directions. Movement of the device 520 in the positiveand negative x-directions (as indicated with the reference coordinatesystem) is limited by the fixed position of the z-pillars and themechanical recess feature 580 that is formed on the underside of thesecond device 520. The range of possible movement of the device 520 inthe +/−x-directions is limited to the distance between the z-pillars 534and the feature 580 at placement. Adequate clearance must be providedbetween the z-pillars spacing and the spacing between the features 580on the device 520. Movement of the device 520 is further limited in they direction by the fixed position of the z-pillar as the mechanicalrecess feature 580 of the device 520 contacts the sidewall of thez-pillar 534 as this device is moved into the aligned position in they-direction shown in FIG. 5C. Movement in the x-direction, in summary,is constrained motion in that the device 520 is free to move in the +/−xdirections within the z-pillar spacing. Movement in the y-direction, insummary, is not initially constrained in that the feature 580 is free tomove in either direction (within a small range) at placement but isconstrained as the feature 580 is brought into contact with the sidewallof the z-pillar 534. Other embodiments and features of embodiments oflateral constraints are further described herein. The lateral constraintshown in FIG. 5 is a lateral constraint that is used to limit the motionof a mounted device such as the mounted device 520 shown in FIG. 5C. Inother embodiments, lateral constraints may be configured to restrict thelateral movement of other devices and can be combined in function withz-pillars to restrict movement laterally and vertically. In someembodiments, the lateral movement of the device 520 is limited bycontact to the sidewall of the recess. In other embodiments, the lateralmovement of the device 520 is limited by contact of the device with aportion of the cavity wall.

An embodiment of a method of fabrication for z-pillars, fiducials, andlateral constraints are described in the process flow of FIG. 6 and thecorresponding sequence of drawings in FIGS. 7A-7P.

Referring to FIG. 6 , a process flowchart is shown for the formation ofinterposer-based PICs with embodiments of the interposer alignmentstructures, and aspects of embodiments described in this flowchart areillustrated in FIG. 7 . In step 690 of process flow 610, a planarwaveguide layer 705 is formed on a base structure, wherein the basestructure 701 includes an optional electrical interconnect layer 703 ona substrate 700. The planar waveguide layer 705 on base structure 701forms interposer 704. The electrical interconnect layer 703, as shown inFIG. 7A is formed in some embodiments on a semiconductor substrate 700such as silicon. Other semiconducting substrates such as indiumphosphide, gallium arsenide, or other semiconductors can also be used.In other embodiments, a ceramic or insulating substrate can be used. Inyet other embodiments, a metal substrate can be used. And in yet otherembodiments, a combination of one or more semiconductor layers,insulating layers, and metal layers are used to form a substrate 700upon which the optional electrical interconnect layer 703 and the planarwaveguide layer 705 are formed. In some embodiments, the electricalinterconnect layer 703 is not in direct contact with the substrate butrather an intervening layer is present. Similarly, the planar waveguidelayer 705, in some embodiments, is not in direct contact with theunderlying electrical interconnect layer 703 but rather an interveninglayer or layers may be present.

In hard mask layer formation step 691 of the process flow 610, apatterned hard mask 716 is formed on the planar waveguide layer 705.Hard mask layer 716 includes patterns for the formation of the opticalwaveguides and all or a portion of the alignment aids from the planarwaveguide layer 705. In the embodiment in FIG. 7B, the alignment aidsinclude the fiducial marks 714, the alignment pillars or z-pillars 734,and a v-groove alignment aid 751. Hard mask layer portion 716 a in FIG.7B shows a hard mask pattern for an embodiment of a z-pillar. Similarly,hard mask portion 716 b shows a hard mask pattern for an embodiment of aplanar waveguide 744. Hard mask portion 716 c shows a hard mask patternfor an embodiment of a fiducial mark 714. And hard mask portion 716 dshows a hard mask pattern for an embodiment of a v-groove alignment aid751. In the embodiments illustrated in FIGS. 7A-7P, the v-groovealignment aid feature 751 is used to position a v-groove for placementof a fiber optic cable as further described herein. In some embodiments,as described herein, the v-groove alignment aid 751 functions as alateral constraint. In the embodiments for the hard mask pattern shownin FIG. 7B, portions of the patterned hard mask include the z-pillarportion 716 a, planar waveguide portion 716 b, fiducial mark portion 716c, and v-groove alignment aid portion 716 d. These portions of the hardmask 716 are used to pattern the z-pillars 734, the planar waveguides744, the fiducial marks 714, and the v-groove alignment aid or lateralconstraint feature 751, respectively, using an etch process to removethe planar waveguide layer 705 from areas not protected by the hard masklayer 716 as shown in FIG. 7C.

Portions of the hard mask layer 716, are also used in some embodimentsto form all or a portion of optical devices 740 for embodiments in whichthe optical devices 740 are formed wholly or in part from the planarwaveguide layer 705. Optical devices 740 may be waveguides, gratings,lens, or any device that can be formed from at least a portion of theplanar waveguide layer. Alternatively, in other embodiments, opticaldevices 740 are mounted devices, and not fabricated directly from theplanar waveguide layer 705 but added at a later step in the process offorming the PIC 702. Optical device 740 can be one or more of a portionof a device formed from the planar waveguide layer and one or more of aportion of a mounted device.

In some embodiments, the planar waveguide layer 705 is formed of one ormore layers of silicon dioxide, silicon nitride, and silicon oxynitrideas described herein. To pattern the planar waveguides from such layersusing a dry etch process, fluorinated etch chemistries in which one ormore commonly utilized gases such as CF₄, CHF₃, C₂F₈, SF₆, among others,are used. In embodiments, aluminum or an alloy of aluminum can be usedto form the hard mask. Aluminum hard masks are known to exhibit a highresistance to dry etching in fluorinated chemistries and thus thedimensions of the hard mask can be maintained during the etching of theplanar waveguide layer 705, in which the fiducial marks 714, thereference pillars, 734, the planar waveguides 744, and the v-groovealignment aid or lateral constraint 751 are formed in Step 692 ofprocess flow 610. A hard mask, as used herein, refers to a non-polymerbased masking layer with a material that has a high resistance to theplasma etch, dry etch, or wet etch, used in the patterning ofsurrounding materials. Aluminum, for example, is an example of a hardmask material in embodiments. Aluminum is a metal layer that has a highresistance to fluorine containing etch chemistries. In otherembodiments, other hard masks are used that also exhibit high resistanceto the etch chemistry such as Au, Ag, Ni, and Pt. In other embodiments,hard masks layers such as Ti, TiO_(x), Ta, TaO_(x), aluminum oxide,silicon nitride, silicon carbide, or a combination of one or more ofthese materials are used. In some embodiments, oxygen or otheroxygen-containing gas is added to the etching chemistry to increase theresistance of the hard mask to the etch chemistry. In yet otherembodiments, diluents are added to the fluorinated gas chemistry such asone or more of argon, helium, nitrogen, and oxygen, among others toincrease the resistance of the hard mask to the fluorinated etchchemistry. In embodiments, the masking layer typically has a slow rateof removal in comparison to the rate of removal of the planar waveguidelayer. Methods for etching of silicon dioxide, silicon nitride, andsilicon oxynitride are well understood by those skilled in the art ofsemiconductor processing, as are methods of increasing the resistance ofaluminum hard mask layers and other hard mask layers using fluorinatedetch chemistries.

After the patterning 692 of the planar waveguide layer to form thefiducial marks 714, the reference pillars 734, the planar waveguides744, and the v-groove alignment aids 751, a mask material is formed overportions of the PIC that includes the hard mask patterned features 716.This mask layer is some embodiments, is a photoresist layer. In otherembodiments, this mask layer is a hard mask layer. In embodiments, themask layer is patterned to expose the underlying patterned hard masklayer portion 716 b over the patterned waveguides 744 and to protect thepatterned hard mask layer portion 716 c over the fiducial marks 714, thepatterned hard mask layer portion 716 a over the reference pillars 734,and optionally the hard mask portion 716 d over the v-groove alignmentaid 751. Exposure of the hard mask layer portion 716 b over thewaveguides, however, enables removal 693 in process flow 610 of the hardmask portion 716 b from the patterned waveguides 744 without the removalof the hard mask portions 716 a, and 716 c from the fiducial marks 714and the z-pillars 734, and optionally from hard mask portion 716 d fromthe v-groove alignment aid 751. In some embodiments, removal of the hardmask portion 716 d may be preferred.

A schematic illustration of features of the PIC after removal of thehard mask portion 716 b and subsequent removal of the mask layer that isused in embodiments to protect the hard mask portions 716 a, 716 c, 716d is shown in FIG. 7D. Removal of the hard mask portion 716 b from theplanar waveguides 744 of the hard mask layer 716 is achieved in someembodiments using a wet etch process that selectively removes the metalor other hard mask with little or no removal of the underlaying planarwaveguide layer. Metal etchants, such as those used for the removal ofan aluminum hard mask, for example, and that have little or no effect onsilicon nitride and silicon dioxide, for example, are well known in theart of semiconductor processing. In other embodiments, a dry etchprocess is used. A benefit of a wet etch process to remove the hard maskportion 716 b from the planar waveguide 744 below includes a highpreferential selectivity for etching of the hard mask 716 with minimalremoval of the underlying planar waveguides 744.

Upon completion of the removal step 693 of the hard mask portion 716 bfrom the planar waveguides 744, and removal of the mask layer that wasused to protect the hard mask portions 716 a, 716 c, and optionally 716d, a forming step 694 is shown in the process flow 610 to form a thickinsulating dielectric layer 738 as illustrated in FIG. 7E. The thickdielectric layer 738 may be one or more layers of silicon dioxide,silicon nitride, or silicon oxynitride, for example, and may include oneor more of a planar waveguide cladding layer, a buffer layer, a spacerlayer, and a passivation layer, among others. In some embodiments, layer738 includes a planarization layer and a planarization step is used toplanarize the thick dielectric layer 738.

Step 695 of the process flow 610 is a forming step that includes theformation of a cavities 748, 749 in the thick dielectric layer 738. Thiscavity forming step 695 can include a patterned hard mask forming stepas illustrated in FIG. 7F and an etching step as illustrated in FIG. 7G,among others. The hard mask 717 shown in FIG. 7F, is preferably one suchas aluminum or from an alloy of aluminum, among others, formed over theinsulating layer 738 and patterned using a plasma etch process or a wetchemical etch process to expose the regions of the underlying insulatinglayer 738 within which cavities 748,749 will be formed. Aluminum andalloys of aluminum, for example, provide a high resistance tofluorinated etchants used to etch insulating layers such as silicondioxide, silicon nitride, and silicon oxynitride preferably used inlayer 738.

In some embodiments, the insulating dielectric layer 738 is formed ofone or more layers of silicon dioxide. In some embodiments, theinsulating dielectric layer 738 is formed of one or more layers ofsilicon dioxide, silicon nitride, and silicon oxynitride. To pattern thelayer 738 and in some embodiments, all or a portion of the underlyinglayers below the layer 738 and all or a portion of the electricalinterconnect layer using a dry etch process, fluorinated etchchemistries in which one or more commonly utilized gases such as CF₄,CHF₃, C₂F₈, SF₆, among others, are used. In embodiments, aluminum or analloy of aluminum is used to form the hard mask. Aluminum hard masks areknown to exhibit a high resistance to dry etching in fluorinatedchemistries and thus the dimensions of the hard mask can be maintainedduring the etching of the dielectric insulating layer 738, in which thereference pillars, the fiducial marks, and other alignment aids areformed in Step 695 of process flow 610. In other embodiments, other hardmasks are used that also exhibit high resistance to the etch chemistrysuch as Au, Ag, Ni, and Pt. In other embodiments, hard masks layers suchas Ti, TiO_(x), Ta, TaO_(x), aluminum oxide, silicon nitride, siliconcarbide, or a combination of one or more of these materials are used. Insome embodiments, oxygen or other oxygen-containing gas is added to theetching chemistry to increase the resistance of the hard mask to theetch chemistry. In yet other embodiments, diluents are added to thefluorinated gas chemistry such as one or more of argon, helium,nitrogen, and oxygen, among others to increase the resistance of thehard mask to the fluorinated etch chemistry. In embodiments, the maskinglayer typically has a slow rate of removal in comparison to the rate ofremoval of the layer 738. Methods for etching of silicon dioxide,silicon nitride, and silicon oxynitride are well understood by thoseskilled in the art of semiconductor processing, as are methods ofincreasing the resistance of aluminum hard mask layers and other hardmask layers using fluorinated etch chemistries.

The effect of the etching step on the formation of the cavity 748,749 isillustrated in FIG. 7G. The z-pillars 734 are shown that result from theexposure of the buried hard mask portion 716 a that was formed from thehard mask 716 in cavity 748. Exposed fiducials 714 are also shown thatresult from the exposure of the buried hard mask portion 716 c that wasformed from the hard mask 716 in cavity 749.

In some embodiments, it is or may not be preferable or necessary toexpose the buried fiducial marks 714 to obtain the improved clarity ofthe fiducials in subsequent steps in which the fiducials 714 are used inthe fabrication of the PIC 702, or for the placement of optical die ontothe PIC 702. In these embodiments, the patterning step for the hard mask717 that is used to expose the areas of the underlying insulating layer738 to form the cavities 748 will not include an allowance for exposureof the areas of the underlying insulating layer 738 to also formcavities 749 to expose the fiducials 714 within these cavities 749 asillustrated in FIG. 7H. Improved visibility of the fiducials 714 is tobe expected upon the formation of the cavity 749, but may not berequired in some embodiments. Improved visibility of the fiducials maynot be required, for example, in embodiments with thin insulating layers738, in applications in which the surface of the thick insulating layer738 remains visibly transparent, and in embodiments in which thecontrast between the fiducials and the underlying layers is adequate.Exposure of the fiducials 714 with the formation of cavity 749, ingeneral, provides improved visibility in embodiments for which thecavities 749 are provided since the focal plane of the fiducial 714 isshared with the focal plane of the z-pillars 734 and other alignmentaids formed using the hard mask 716. The improved visibility alsoresults from the elimination of the effects that processing steps suchas mechanical planarization or other process effects that may increasethe opacity of the layer 738 that might limit visibility of a buriedfiducial. In the embodiment illustrated in FIG. 7G, the alignmentpillars 734 are shown in cavity 748 and the fiducials 714 are shown incavity 749. In other embodiments, the fiducials 714 are formed in thesame cavity 748 as the alignment reference pillars 734. In otherembodiments, two or more fiducial marks 714 are formed. In embodimentswith two or more fiducial marks 714, one or more fiducial marks 714 maybe formed within the cavity 748 and one or more fiducial marks 714 maybe formed in a separate cavity 749. In yet other embodiments with two ormore fiducial marks 714, multiple cavities 749 are formed with fiducialmarks 714. The fiducial marks 714 illustrated herein are shown in theshape of a “+” sign. Other shapes are also used in embodiments.Effective shapes for fiducial marks are well understood by those skilledin the art. Fiducial markings may also be formed using features formedin the hard mask layer that have other structural or photonic functions.

Also shown in the embodiments in FIG. 7G and FIG. 7H, is the v-groovealignment aid 751. This v-groove alignment aid 751 is exposed in theseembodiments using the same patterned hard mask 717 and etch process usedin the formation of one or more of the cavities 748, 749. An aspect ofembodiments is the use of a common lithographic patterning step todefine the v-groove alignment aid 751 with the planar waveguide 744 toprovide lithographic level of alignment between these features of a PICusing the techniques described herein. The v-groove is used inembodiments to position a fiber optic cable, the core of which isaligned in embodiments with a portion of a planar waveguide 744. Andalthough the patterning of the v-groove alignment aid 751 from theplanar waveguide layer, in embodiments, is performed concurrently withthe patterning of the fiducials 714, the planar waveguides 744, and thez-pillars 734, the subsequent removal of the oxide 738 to expose thev-groove alignment feature 751 from within the oxide 738 need not beperformed concurrently with the formation of the cavities 748, 749.

In the schematic drawing in FIG. 7I, the PIC 702 is shown in embodimentsafter removal of the hard mask 717 used in the formation of the cavities748,749 in the insulating layer 738, and removal of the oxide 738 inproximity to the alignment aid 751 as shown, for example, in the FIG.7I.

Prior to completion of the PIC 702, the v-grooves that are commonlyformed on the PIC substrates to accommodate the attachment of fiberoptic cables for the delivery and extraction of optical signals from thePIC 702 are typically formed. FIG. 7J and FIG. 7K show an embodiment ofa method for forming the v-groove using the alignment aid 751 patternedfrom the planar waveguide layer 705. Significant advantages to thealignment of the core of the fiber optic cable with waveguide facet 752of the planar waveguides 744 formed in the planar waveguide layer 705are enabled with embodiments described herein. The use of the patternedplanar waveguide layer 705 to simultaneously form the alignment aid 751and to form the waveguides 744, provides lithographic-level resolutionfor the ultimate alignment of the fiber optic core 756 placed within thev-groove alignment aid 751 and the waveguide facet 752 of the planarwaveguides 744 to which the core 756 of a fiber optic cable 754 isaligned. In the embodiment shown in FIG. 7J, a patterned PR mask is usedto expose the portion of the substrate for the formation of one or morev-grooves in the area of the substrate within the alignment aid 751.This patterned photoresist mask 753 protects at least a portion of thePIC during the formation of the v-grooves 750. The etch process forforming v-grooves is well understood in the art of semiconductorfabrication and is typically formed using a wet etch process.

Referring to FIG. 7K, an embodiment of the PIC 702 is shown afterformation of the v-groove 750 and removal of the photoresist mask 753.Surfaces within the v-groove 750 form a contact with the cladding layer755 of a mounted fiber optic cable 754. FIG. 7L shows the PIC 702 with aportion of a fiber optic cable 754 positioned in the v-groove 750 toillustrate the alignment of the fiber optic cable core 756 with the endfacet 752 (shown in FIG. 7K) of the portion of the planar waveguide 744to which the core 756 is aligned. Alignment of the fiber core 756 withthe waveguide facet 752 of the planar waveguide 744 is necessary forefficient transfer of optical signals between these devices.

It should be noted that the v-grooves 750 are typically formed prior tothe completion of the PIC fabrication process, and that the fiber opticcables 754 are typically not mounted to the PIC 702 until after thecompletion of the PIC fabrication process and including the completionof the singulation of the substrate into individual PIC die. Thepositioning of the fiber optic cable 754 into the v-groove 750, however,is shown in FIG. 7L to illustrate the alignment of the core 756 of thefiber optic cable 754 with the core of the planar waveguide 744 and thebenefit of forming the alignment aid 751 lithographically with theplanar waveguide 744.

The sequence of drawings in FIGS. 7A-7L illustrate the formation ofelements of a self-aligned optoelectrical device structure in aninterposer-based PIC 702 and include the z-pillars 734 in cavities 748,the buried planar waveguide structures 744 that terminate at the wallsof the cavity 748, and the buried fiducial marks 714. The sequence ofdrawings in FIGS. 7A-7L also illustrate the formation of an embodimentof a form of v-groove or lateral constraint alignment aid 751 used inthe positioning of a v-groove 750 relative to an end facet 752 of aportion of a planar waveguide 744. Upon formation of the elements of thePIC structure 702 as shown, the implementation of the alignment featuresin embodiments in which optical die are positioned into the PIC 702 arethusly demonstrated in FIG. 7M-7P.

Referring to FIG. 7M, a perspective drawing is shown of an embodiment ofan optoelectrical die 720. Optoelectrical die 720 in some embodiments isan optical emitting device such as a laser, or a photodiode, forexample. In other embodiments, photoelectrical die 720 is a receivingdevice such as a photodiode or other form of photodetector. In yet otherembodiments, the device 720 is an optical device such as a waveguide ora grating. Examples of waveguide devices include spot size convertersand arrayed waveguides, among others. Other examples of waveguidedevices include waveguides through which optical signals are propagated,routed, modulated, focused, transformed, or otherwise included in aphotonic circuit to receive, direct, modify and carry optical signalswithin all or a portion of the photonic circuit. In yet otherembodiments, the device 720 is an echelle grating or other form ofgrating. In yet other embodiments, the device 720 is a lens. Device 720can be any optical or optoelectrical device that can be formed into adie that can be mounted using the alignment features described herein.

Die 720 is shown in FIG. 7M with facet 778. Facet 778 is a surface ofthe device 720 through which an optical function of the device 720 isaccessed or interfaced external to the device 720. Facet 778 forembodiments in which the device 720 is a laser, for example, is thesurface through which the optical signal from the laser is emitted. Forembodiments in which the device 720 is a photodetector, for example,facet 779 is the surface through which the optical signal is received orotherwise detected. Also shown in FIG. 7M is the optical axes of device720 that include the horizontal axis 707 a and the vertical axis 708 a.The axes are shown in the embodiment in FIG. 7M at the center of anoptical signal on the facet 778 of device 720 and the alignment of axessuch as those shown in FIG. 7M with axes of other devices in PICs arefurther described herein.

Referring to FIG. 7N, aspects of the process of utilizing the alignmentfeatures described herein to place optoelectrical die 720 into thecavities 748 of the PIC 702 and to align the optical and electricalfeatures of the placed optoelectrical die 720 to the optical andelectrical circuit features on the PIC 702 are described. FIG. 7N showsa schematic drawing of the interposer-based PIC 702 after placement of afirst optoelectrical die 720 a. Optoelectrical die 720 a is, forexample, a laser die. The optoelectrical die 720 a can be placed with ahigh degree of accuracy into the cavity 748 and within the spacingbetween the alignment reference pillars 734. This high placementaccuracy is enabled, in embodiments, as a consequence of having formedthe fiducial marks 714 and the z-pillars 734 using the same lithographicprocess and hard mask 716. Use of the same lithographic process and hardmask 716 for the fiducials 714 and the reference pillars 734 providesfor precisely referenced mechanical alignment pillars 734 relative tothe fiducial marks 714 for features that are formed from a common planarwaveguide layer 705. Maintaining the visibility of the buried fiducials714 is accomplished in embodiments, for example, with the use of amasking and etch process to expose the buried fiducials 714. In otherembodiments, thin transparent insulating films 738 are used over thefiducials 714 to maintain visibility of the fiducial marks 714 inembodiments in which the fiducials 714 and the z-pillars 734 arepatterned and formed from the same hard mask layer 716. Maintaining thevisibility of the fiducials is beneficial for achieving high resolutionin the placement of the optoelectrical die 720 in automated dieplacement equipment, for example. In the embodiment shown in FIG. 7N,the fiducials have been exposed from within the insulating layer 738with the formation of the cavity 739.

In the embodiment illustrated in FIG. 7N, placement of a firstoptoelectrical die 720 a is followed by the placement of a secondoptoelectrical die 720 b as illustrated in FIG. 7O. In the embodimentshown in FIG. 7N and FIG. 7O, a cavity 748 is shown for which allowancesare made to accommodate two optoelectrical die 720 a, 720 b. In otherembodiments, more than two optoelectrical die 720 are accommodatedwithin a cavity 748 and following placement of the second die 720 b, theadditional optoelectrical die 720 are positioned within the cavity. Inother embodiments, cavity 748 accommodates only a single optoelectricaldie 720 a and thus only a single optoelectrical die 720 a is placed inthe cavity 748. In these and other embodiments, the optoelectrical die720 includes one or more optoelectrical emitting devices such as a laseror an LED, for example, among others, or one or more optoelectricalreceiving devices such as a photodetector, for example, among others. Inother embodiments, the optoelectrical die 720 includes one or moreoptoelectrical emitting devices and one or more optoelectrical receivingdevices. In other embodiments, the optoelectrical die 720 includes oneor more optical devices.

In embodiments, after placement, the optical and electrical features ofthe optoelectrical die 720 a, 720 b that have been placed into thecavities 748 require alignment with the optical and electrical featureson the interposer-based PIC 702. The arrows shown in FIG. 7P indicatethe direction of motion of the optoelectrical die 720, in the embodimentshown, upon initiation of an alignment step in which one or more opticaland electrical features are brought into alignment between theoptoelectrical die 720 and the optical and electrical features of theinterposer-based PIC 702. The positioning of the optoelectrical die 720over the z-pillars 734 using the fiducial marks 714 for lateralreference provides for the subsequent alignment with the other featuresand devices formed in the planar waveguide layer 705. The co-formationof the fiducials 714 and the z-pillars 734 from the planar waveguidelayer 705 enables precise alignment of the mounted die 720 on theinterposer-based PIC 702 with portions of the planar waveguides 744. Inthe embodiment shown in FIG. 7P, facets 778 of the mountedoptoelectrical die 720 are moved into alignment with the facets 752 ofthe planar waveguides that intersect with the wall of the cavity 748.Additional details are provided herein for the placement, alignment, andassociated steps, with additional details on specific aspects ofembodiments of the alignment aids on interposer-based PIC devices 702.

Referring to FIGS. 7Q and 7R, a sequence of drawings is shown thatillustrate a method that can be utilized in the alignment of optical andoptoelectrical devices in embodiments, as for example, the alignmentprocedure described for mounted devices 720 a and 720 b shown in FIGS.7N-7P.

A lateral force can be formed on mating devices or die by bringing intoproximity, pairs of solder contact layers on mating surfaces, and toraise the temperature of the solder until the solder melts, after whichsurface tension in the liquid solder acts to pull the two contactstoward one another. The lateral force is formed when the solder contactsurfaces, misaligned at placement, act to be brought into arealalignment. An approach utilizing this principal is illustrated in FIG.7Q as it applies to embodiments for bringing the optical and electricalfeatures of the optoelectrical die 720 a, 720 b, for example, intoalignment with optical and electrical features of the interposer-basedPIC 702.

In FIG. 7Q(i), a schematic drawing of an embodiment of an optoelectricaldevice or die 720 is shown with this device 720 positioned over thecavity of an interposer-based PIC 702. Solder layer 730 a, formed forexample, as shown on an electrical contact of the optoelectrical die720, is misaligned at placement with solder layer 730 b on the matingcontact of the interposer-based PIC 702 as the optoelectrical die 720 isplaced into the cavity 748. The misaligned solder layer 730 a on theoptoelectrical die 720 and the solder layer 730 b in the interposercavity 748 are shown in FIG. 7Q(ii) after placement over the z-pillars734 of the optoelectrical die 720 into the cavity 748 of the interposer,further showing the intentional misalignment of the solder layers afterplacement. In some embodiments, after one or more die have been placedonto the interposer, a heating source is applied to the structure suchthat the solder layer 730 a and solder layer 730 b are raised intemperature above the solder melting temperature. As the solder meltsand the solder layer from each contact is combined into a single moltencontact 731 as illustrated in FIG. 7Q(iii), the surface tension in themolten solder will cause lateral movement of the optoelectrical die 720in a direction such that the two misaligned electrical contacts will bebrought into further areal alignment which then causes the spacingbetween the optical features of the optical die 720 and the planarwaveguide 744 to be reduced. Movement of the die (in the direction ofthe large arrow in FIG. 7Q(iii)) is expected to continue, for example,until the motion is blocked by contact between the optoelectrical die720 with the cavity wall 748, motion is blocked by contact between afeature of the optoelectrical die 720 and an obstacle such as anintentionally positioned stop or lateral constraint on the interposer,until the contacts of the interposer and the optoelectrical die aresubstantially aligned, or until the heating source is removed. In FIG.7Q(iv), the movement of the optoelectrical die 720 is shown to have beenhalted by contact between the wall of the cavity 748 and the substrateof the optoelectrical die 720 after the optical and mechanical featuresof the optoelectrical die 720 have been brought into alignment with theoptical features of the interposer-based PIC 702. The large arrow isshown to have reached the dimension line in the FIG. 7Q(iv). FIGS.7Q(ii)-7Q(iii) show the core of waveguide 744, for example, withwaveguide core 758 in alignment with the optical feature 774 of opticaldevice 720. The optical axis of the device 720 is typically containedwith the optical feature 774 of the device 720.

FIG. 7R(i) shows a top-down view and FIG. 7R(ii) shows a cross sectionalview of the cross section shown in FIG. 7Q(iv) to further illustrateaspects of the solder melt process in the alignment of the opticalfeatures of the optical device 720 with a planar waveguide 744 on theinterposer portion of a PIC 720. The top-down view shows the z-pillars734 on the interposer substrate and the alignment features 780 on theoptical die 720 that guide the optical die 720 into the aligned positionin the cavity 748 during the alignment process for the alignment processshown in FIGS. 7Q(i)-7Q(iv). Other alignment processes may also be usedin other embodiments. The dotted line with label “720 (at placement)”shown in the top-down view in FIG. 7R(i) shows the edge of the die 720at placement in the embodiments and solid edge labeled “720 (afterpositioning)” shows the position of the device 720 after alignment.

Alignment of optical features on the optoelectrical die 740 with opticalfeatures on the interposer is required in PICs, for example, to ensurethat optical signals can be exchanged between the interposer-based PIC702 and the mounted optoelectrical die 720. Optical signal 770 in FIGS.7R(i) and FIG. 7R(ii) is shown propagating from the optical feature 774of device 720, for example, to the core 758 of a planar waveguide 744 onthe interposer-based PIC 702. An optical feature on a laser, forexample, is the emitting facet of the laser where the optical signal isemitted. An optical feature on a photodetector, in another example, isthe facet or surface of the photodetector on which the light isreceived.

It should be noted that the procedure for alignment utilizing themelting of solder as described in FIG. 7Q can be utilized in embodimentsfor both optical and optoelectrical devices regardless of whether or notthe contact formed with the solder functions as an electrical contact toan underlying electrical interconnect. For optical devices, for example,PICs 702 may be configured with the solder contacts but these contactsmay not be used to form an electrical contact for devices that do nothave an electrical feature or that require an electrical input oroutput, as in for example, a grating, a lens, or other optical device.In optoelectrical devices such as a laser or a photodetector, the solderconnections described in FIGS. 7Q and 7R are utilized for alignment ofthe facets of these devices with optical features on the PICs 702 and toform an electrical contact with the underlying electrical interconnectsin the electrical interconnect layer 703.

In some embodiments for alignment of devices that utilize the alignmentfeatures and methods described herein, a heating source is applied tothe one or more of the solder layers 730 a, 730 b after one or moreoptoelectrical die 720 have been placed into cavities 748 on theinterposer-based PIC 702. This and other examples of embodiments forapplying heat to the solder layer 730 a and solder layer 730 b arefurther illustrated in FIG. 7S. In FIG. 7S(i), interposer-based PIC 702with one or more optoelectrical die 720 is positioned on a platen 782and exposed to a heating source 783. The heating source 783 is used toraise the temperature of the solder layers 730 a, 730 b. Heating sources783, as described herein, are any one or more of an electricallyresistive heating source, a radiative heat source such as an IR lamp orother photon source, a heated air or other gas source, and one or morelasers, among others. In FIG. 7S(ii), a second heat source 783 isapplied over the interposer-based PIC 702 in addition to the heat source783 positioned below the substrate 702 as shown. In embodiments shown inFIG. 7S(ii), heating is applied to the substrate 702, simultaneously orasynchronistically both below and above the PIC substrate 702. Theheating source 730 a heats the PIC 702 from below and heating source 730b heats the PIC 702 from above as shown and directly heats theoptoelectrical die 720. Embodiments, as illustrated in FIG. 7S includethose embodiments in which one of the heat sources 783 a, 783 b is notpresent or not active. In yet other embodiments, as shown in FIG.7S(iii), a local heat source is applied to the optoelectrical die 720 toheat the solder connections 730 a, 730 b. In these embodiments, heatingis provided to one or more optoelectrical die 720 from a localized heatsource 783 such as from a laser, or focused optical source. Heating ofthe solder connections 730 a, 730 b in these embodiments, are beneficialin that the heating can be performed as the optoelectrical die are beingplaced on the PIC substrate 702. In some embodiments, a first heatingstep can be applied to the solder connection forming a temporary bondwithout a full alignment step. Laser tacking can be performed veryquickly, and once all of the devices are tacked into place, an entiresubstrate with a multitude of tacked die can be heated together toperform the longer alignment step. In embodiments, the time totemporarily position a die in place can be on the order of less than asecond to a couple of seconds, whereas the alignment steps can take upto 10 seconds or longer. Tacking the die in place using a tackingconfiguration, can result in considerable time savings when thealignment steps are performed at the wafer level after a multitude ofdie have been placed. Post tacking processes benefit from the use of thecaptured lateral alignment features such as the captured features shownin FIG. 5C, for example, in which the z-pillars on the interposer aresurrounded by a recess formed on the attached die. The post tackingheating steps can be performed in all or portions of wafer level heatingapparatuses such as those shown in FIGS. 7S(i), 7S(ii), 7S(iv), and7S(v). In FIG. 7S(iv), embodiments are shown in which a heating source783 a provides heat below the PIC substrate 702 and is combined with alocalized heat source 783 b. In some embodiments illustrated in FIG.7S(iv), the heating source 783 a raises the temperature of the PICsubstrate 702 such that the solder layers 730 a, 730 b are raised abovethe melting temperature to initiate the alignment of the optoelectricaldie 720. In other embodiments illustrated in FIG. 7S(iv), the heatingsource 783 a does not raise the temperature of the PIC substrate 702 andthe solder layers 730 a, 730 b above the melting temperature but theheating source 783 a raises the temperature of the PIC substrate 702partly and the local heating source 783 b is used to provide theadditional rise in the temperature above the solder melting temperature.For example, if the melting temperature of the solder layers 730 a, 730b is 180° C., the heating source 783 a is used in this example to raisethe temperature of the platen to 175° C., and the localized heat source783 b is used to further raise the temperature such that the temperatureof the solder layers 730 a, 730 b is above 180° C. required to melt thesolder and cause the alignment of the optoelectrical die 720 with theinterposer-based PIC 702. And in yet other embodiments, as illustratedin FIG. 7(v), one or more interposer-based PICs 702 are placed into atemperature-controlled environment 784, such as an oven, to raise thetemperature of the solder layers 730 a, 730 b and to cause the alignmentof the optoelectrical die 720 with the interposer-based PIC 702.

In some embodiments, the substrate is exposed to a heating source afterthe placement of the optoelectrical die 720 into the cavity 748. Thisalignment step can be performed immediately upon placement or after oneor more die have been placed, or after all of the die 720 have beenplaced onto the interposer-based PIC 702. In some embodiments in whichthe alignment step is performed immediately after placement, thealignment is accomplished, for example, by applying a source of heat tothe interposer substrate during the placement process. In otherembodiments, a source of heating of the substrate is applied after oneor more of the optoelectrical die 720 have been placed onto theinterposer. It is advantageous, for example, in some embodiments, toplace all of the die onto the interposer substrate, or to place all ofone type of optoelectrical die in embodiments for which multiple typesof die are placed onto the interposer substrate, and to then apply aheating source to perform an alignment step for all of the die for whichalignment is required. In some embodiments for which multiple types ofdevices are placed into the cavities 748 of the interposer substrate andfor which alignment is required, solder layers 730 with a meltingtemperature that is the same as that used for subsequent layers is usedfor the first set of devices that are placed and aligned onto thesubstrate. In other embodiments for which multiple types of devices areplaced into the cavities 748 of the interposer substrate and for whichalignment is required, a solder layer 730 with a melting temperaturethat is higher than that used for subsequent layers is used for thefirst set of devices that are placed and aligned onto the substrate. Useof decreasing solder melting temperatures in subsequent alignment stepscan reduce or eliminate the minimize the effect of the heating duringsubsequent alignment steps on previously aligned optoelectrical die 720.

In some embodiments, many or all of the optoelectrical die 720 areplaced into the cavities 748 on the interposer-based substrate 702 priorto heating and then the wafer is heated using one of the heatingconfigurations shown schematically in FIG. 7S(i)-7S(v), or some otherheating configuration. In other embodiments, a single optoelectrical die720 or a small number of optoelectrical die 720 are placed onto theinterposer-based PIC 702 and then heated locally using a heatingconfiguration such as the configuration shown in FIGS. 7S(iii) and7S(iv), for example, or another heating configuration.

In other embodiments, a first set of optoelectrical die 720 with a firstsolder type with a first melting temperature are placed into thecavities 748 on the interposer-based substrate 702 and then heated to afirst temperature to cause the alignment of the electrical and opticalfeatures of the optoelectrical die 720 with the optical and electricalfeatures of the interposer-based PIC 702. A second set of optoelectricaldie 720 with a second solder type with a second melting temperature areplaced into the cavities 748 on the interposer-based substrate 702 andthen heated to a second temperature, lower than the first temperature,to cause the alignment of the electrical and optical features of theoptoelectrical die 720 with the optical and electrical features of theinterposer-based PIC 702. In yet other embodiments, additional sets ofoptoelectrical devices with additional solder types, each set utilizinga solder with a reduced melting temperature than the prior set, areplaced into the cavities 748 of the interposer-based PIC 702 and heatedto cause the alignment of the optoelectrical die 720.

Referring to FIG. 7T, an embodiment of an optoelectrical die 720 on aninterposer-based PIC 702 is schematically shown. The embodiment showsone of multiple PIC devices formed on a substrate using semiconductorfabrication methods in which a multitude of devices are formed on alarge wafer or substrate using integrated wafer scale processingtechniques. In the embodiment shown in FIG. 7T of an optoelectrical die720 on an interposer substrate, the figure shows a mounted device afterheating and melting of the solder layers 730 a, 730 b shown in FIG.7S(i)-7S(v) to form the melded solder connection 731 shown in FIG. 7T.The optical and electrical features of the optoelectrical die 720 havealigned, after the heating and alignment steps, with the optical andelectrical features of the interposer-based PIC 702. Note that themounted optoelectrical die 720 has moved to the left as shown in FIG.7T, and in this embodiment, has made contact with the wall of the cavity748. The optical feature of the optoelectrical die 720, such as theemitting facet of a laser for example, is shown aligned with the exposedfacet of planar waveguide 744 on the interposer-based PIC 702. In otherembodiments, the optical device is aligned when making contact with alateral constraint.

In some embodiments, placement of the optoelectrical die 720 into theinterposer cavities 748 and subsequent heating of the solder layers 730a, 730 b on the PIC interposer substrate 702 is done prior tosingulation of the substrate into individual PIC die 702. In otherembodiments, placement of the optoelectrical die 720 into the interposercavities 748 and subsequent heating of the solder layers 730 a, 730 b onthe PIC interposer substrate 702 is performed after singulation of thesubstrate into individual die.

Embodiments of the alignment aids described herein can be formed in arange of configurations and can include variations in the quantities,the shapes, the lateral positions, and the vertical positions of thesealignment aids. Embodiments showing variations in the quantities andpositions of the z-pillar alignment aids is presented in FIG. 8 .Further variations in the shape and positioning of some embodiments forthe lateral constraint alignment aids are presented in FIGS. 9-10 . Itshould be noted, that additional variations in the shape and positioningof the z-pillars and the lateral alignment aids can be anticipated fromthe embodiments shown, and that other shapes, positions, and quantitiesfor the z-pillars and the lateral alignment aids remain within the scopeof embodiments.

Referring to FIGS. 8A-8C, embodiments in which the quantity and positionof z-pillar alignment aids are varied are shown. In FIG. 8A(i), a commoncross-sectional schematic view of a PIC 802 is shown with optical device820 mounted in cavity 848 on optical device 812. The optical device 812is a buried planar waveguide formed on the substrate 800. The horizontaloptical axes 807 a, 807 b of these devices 812, 820 are shown inalignment, resulting largely from the contact of the mechanicalreference plane 826ref of the optical device 820 with the top of thez-pillar 834, taking into account the offset between the mechanicalreference plane 826ref and the optical axis of the device 820. Alsoshown in FIG. 8A is the fiducial 814 formed in cavity 849. Referencefeature 826ref of the device 820 forms a contact with the 825ref featureat the top of the z-pillar 834. An offset is shown between the opticalaxis 807 of the PIC 802 and the reference features 825ref at the top ofthe z-pillar and the 826ref of the device 820. The PIC structure in FIG.8A shows an embodiment, for example, for which the fiducial 814, one ormore z-pillars 834, and the planar waveguide layer of device 812 areformed using the same lithographic patterning step and hard mask layeras described in FIG. 6 and FIG. 7 .

Referring to FIG. 8A(ii), a top down view of a structure with a singlez-pillar 834 is shown. The top down view shows an example of thepositioning of a single z-pillar 834. Also shown in the FIG. 8A(ii) isthe fiducial 814. The vertical optical axes 808 a, 808 b are shown inalignment. Similarly, in FIG. 8A(iii), a top down view of a structurewith two z-pillars 834 is shown. The top down view shows an example ofthe positioning of two z-pillars 834. Also shown in the FIG. 8A(iii) arethe fiducial 814 and the aligned vertical optical axes 808 a, 808 b ofdevices 812, 820, respectively. In some embodiments, a greater quantityof alignment pillars can lead to an increase in the stability andintegrity of the mounting of the optical devices 820.

Other examples of configurations with variations in the quantities andpositions of z-pillars are shown in FIG. 8B. FIG. 8B(i) shows a commoncross-sectional schematic for the top-down views shown in FIGS. 8B(ii),8B(iii), and 8B(iv). The top-down views in FIGS. 8B(ii), 8B(iii), and8B(iv) show examples of embodiments with three, four, and fivez-pillars, respectively. The quantity and positioning of the z-pillars834 affects the alignment and stability of the devices 820 that aremounted over the z-pillar alignment aids 834. And the number andpositioning of the z-pillars can, in general, be influenced by the sizeand shape of the mounted device 820. Also shown in the FIG. 8A(iii) arethe fiducial 814 and the aligned vertical optical axes 808 a, 808 b ofdevices 812, 820, respectively.

And in yet other examples of variations in the quantity and positioningof z-pillars in embodiments is shown in FIGS. 8C(i), 8C(ii), and8C(iii). In FIG. 8C(i), a common cross-sectional schematic view of PIC802 for the top-down views shown in FIGS. 8C(ii) and 8C(iii) that showstructures with six and seven z-pillar alignment aids, respectively.

In some embodiments, only a single z-pillar 834 is required to achievesubstantial alignment between the horizontal optical axes 807 a, 807 b.In other embodiments, multiple z-pillars 834 are required. In general,as the quantity of z-pillar alignment aids 834 is increased in supportof the device 820, the stability of the device 820 is expected toimprove. Too many z-pillars 834, however, can increase the surfaceresistance required to overcome as the device is moved into finalaligned position as described herein.

In addition to the quantity and positioning of the z-pillars 834,additional latitude is provided in the shapes of the z-pillar, resultingin the formation of lateral constraints from the z-pillars, and in thequantity of z-pillars heights that can be provided using embodiments ofthe structures and techniques described herein. In the followingsection, examples of embodiments with variations in the shapes of thez-pillar alignment aids and the role of the shape in the formation oflateral constraints is further described.

An example of an embodiment of a PIC formed with lateral constraintsusing the z-pillar alignment aids was previously described in theembodiment in FIG. 5C. Another example embodiment is shown with greaterdetail in FIG. 9A. In FIG. 9A(i), a top-down view of a PIC 902 showslateral constraint alignment aids 981 that are also shown in FIG. 9A(ii)in cross section (Section A-A′). In the embodiment shown, the z-pillaralignment aid 934 when combined with a compatible feature 980 on theoptical die 920 further forms a lateral constraint alignment aid 981that constrains the movement of the optical die 920 on the device 912 inthe lateral directions, in addition to the vertical alignment feature ofthe z-pillar 934. In embodiments, the cavity 948 within which opticaldevice 920 mounted is formed in dielectric layer 938 and in someembodiments, may extend into the electrical interconnect layer 903.

In a first lateral direction, the x-direction, the lateral constraintportion of the z-pillar alignment aid 934 facilitates a restriction inthe range of positions in the cavity 948 over which the device 920 canoccupy. The width of the body 946 of the optical device 920 incombination with the x-direction spacing between the two z-pillars formsa mechanical constraint that restricts the movement of the device 920 inthe x-direction. The device 920 is free to move unrestricted between thetwo z-pillars but cannot move beyond the point in either the +x or −xdirections at which contact is made between one of the z-pillars 934 andthe body 946 of the device 920. In the x-direction, an alignment isachieved within the tolerances of the placement and clearance betweenthe two z-pillars shown. The label showing the “Lateral constraint in+/−x direction” in the figure shows the width of a mechanical feature onthe device 920 that must be positioned between the z-pillars 934. Thisfeature must be small enough to allow clearance for placement of thedevice 920 into the cavity without inducing a collision between thedevice 920 and either of the z-pillars 934.

In a second lateral direction, the y-direction, the lateral constraintportion of the z-pillar alignment aids facilitate the guided movementand ultimate spacing between optical devices 912, 920. Upon placement ofthe device 920, and prior to alignment in the y-direction, the positionof the device 920 is indicated by a dotted line in the top-down view ofFIG. 9A(i) with label “Note A”. Prior to alignment, the feature 980 isnot in contact with the z-pillar 934. After alignment, the device 920 ismoved into position to the right (+y-direction) until contact is madebetween the alignment pillar 934 on device 912 and the alignment feature980 of the device 920 to achieve the y-direction alignment. The spacingbetween devices in FIG. 9A is denoted as “Design spacing iny-direction”. The top-down view in FIG. 9A(i) shows square-shapedz-pillars within rectangular cavities having wall 980. In forming acontact with the wall 980 of device 920, the z-pillar alignment aid 934restricts the movement in the y-direction. Prior to forming a contactwith the wall 980, the device 920 is free to move within the range ofmotion afforded by the cavity in the device 920. In embodiments, apreferred location is commonly identified for optimal signal transferbetween the optical devices 912, 920 and a lateral constraint design isimplemented that enables the movement to this preferred position. InFIG. 9A, for example, a preferred design spacing is shown with lateralspacing between devices as indicated by the “design spacing iny-direction.” The spacing shown is achieved in the example embodiment asa result of the contact that is formed between the wall 980 of the leftside of the cavity in device 920 as shown in FIG. 9A(ii) and the leftside of the z-pillar 934 (this location is identified as the “lateralconstraint in the +y-direction” in top-down view in FIG. 9A(i). Thelithographic level precision resulting from the co-formation of thewaveguides 944, the z-pillars 934, and the fiducial 914 yieldslithographic level precision in the achievable positioning of themounted device 920 on the device 912 and the subsequent alignment of theoptical axes and spacing of the optical devices 912, 920. In summary,the effective alignment of the two optical devices 912, 920 for optimalsignal transfer, for example, requires alignment of the horizontal axes907 a, 907 b of the two devices 912, 920, the vertical axes 908 a, 908 bof the two devices 912, 920, and the spacing between the two device 912,920. The lateral constraint feature of the z-pillar alignment aidsprovides a structure and method for achieving such alignment.

It should be noted that the use of the z-pillar alignment aids 934 foralignment of the devices 912, 920 in the z-direction is typicallyunaffected by the addition of the lateral constraint features of thez-pillars 934. The alignment of the horizontal axes of the opticalsignal planes are determined in embodiments by the vertical heights ofthe optical axes of the devices 912, 920. The height of the opticaldevice 920 is determined in the embodiment shown in FIG. 9A by themechanical feature of the device 920 labeled with reference plane 926refthat forms a contact with the top surface of the z-pillar 934 at thereference plane 925ref. This surface to surface contact provides a highlevel of accuracy in the ultimate vertical position of the device 920,and subsequently to the alignment of the optical axis 907 b of thisdevice 920 with the optical axis 907 a of the device 912.

Upon positioning of the body of the device 920 between and over thez-pillars 934, the device 920 is positioned vertically as contact isformed between the top of the z-pillar 934 and the mechanical feature atthe reference plane 926ref of device 920. Upon positioning, the movementof device 920 is also constrained in the +x and −x directions asdetermined by the spacing between the z-pillars in the x-direction andby the width of the portion of the device 920 that resides between thez-pillars. The allowed movement of the device 920 between the z-pillarsin the x-direction, in embodiments, is such that the width of the planarwaveguide 944 of device 912 is sufficient to receive the optical signal970 from a sending device such as a laser. Furthermore, upon placement,the device 920 is free to move within a narrow range in the +y and −ydirections but is ultimately guided into position in the +y-direction asshown using techniques further described herein until reaching aconstrained position as determined by the requirements of the aligneddevices. Placement of the device 920 into the cavity is accomplished inembodiments, using offsets, such as offset x and offset y relative tothe fiducials to establish the location for placing the device 920using, for example, automated die placement equipment.

The fiducial 914 in cavity 949 is shown formed at the same focal plane909 as the top of the z-pillar 934. Portions of the hard mask 916include the z-pillar portion 916 a and the fiducial portion 916 c. Theplanar waveguide portion of the hard mask 916 is removed in embodiments,as was shown in FIG. 7D. Contained within the planar waveguide 944 isoptical axis 907 a of the device 912, and this optical axis 907 a alignswith the optical axis 907 b as the device 920 is moved into alignmentwithin the cavity 948. In the embodiment shown in FIG. 9A, opticaldevice 920 may be an emitting device 920, such as a laser. Inembodiments that include an emitting device, an optical signal 970 willbe emitted from the device 920 and be received by the planar waveguideportion 944 that intersects the cavity 948. An optical signal 970 isshown in FIG. 9A(ii).

Another example embodiment is shown in FIG. 9B. In FIG. 9B(i), atop-down view of a PIC 902 shows lateral constraint alignment aids 981that are also shown in FIG. 9B(ii) in cross section (Section B-B′). Inthe embodiment shown, the z-pillar alignment aid 934 when combined witha compatible feature 980 on the optical die 920 further forms a lateralconstraint alignment aid 981 that constrains the movement of the opticaldie 920 on the device 912 in the lateral directions, in addition to thevertical alignment feature of the z-pillar 934. In embodiments, thecavity 948 within which optical device 920 mounted is formed indielectric layer 938 and in some embodiments, may extend into theelectrical interconnect layer 903.

In a first lateral direction, the x-direction, the lateral constraintportion of the z-pillar alignment aid 934 facilitates a restriction inthe range of positions in the cavity 948 over which the device 920 canoccupy. The width of the body 946 of the optical device 920 incombination with the x-direction spacing between the two sets ofz-pillars 934 a, 934 b forms a mechanical constraint that restricts themovement of the device 920 in the x-direction. The device 920 isinitially free to move unrestricted between the two sets of z-pillarsbut cannot move beyond the point in either the +x or −x directions atwhich contact is made between one of the z-pillars 934 a, 934 b and thebody 946 of the device 920. In the x-direction, an alignment isinitially achieved within the tolerances of the placement and clearancebetween the two sets of z-pillars 934 a, 934 b shown. The label showingthe “Lateral constraint in +/−x direction” in the figure shows the widthof a mechanical feature on the device 920 that must be positionedbetween the z-pillars 934. This feature must be small enough to allowclearance for placement of the device 920 into the cavity withoutinducing a collision between the device 920 and either of the z-pillars934 during placement and is typically determined by the placementaccuracy of the placement equipment.

In a second lateral direction, the y-direction, the lateral constraintportion of the z-pillar alignment aids facilitate the guided movementand ultimate spacing between optical devices 912, 920. Upon placement ofthe device 920, and prior to alignment in the y-direction, the positionof the device 920 is indicated by a dotted line in the top-down view ofFIG. 9A(i) with label “Note A”. Prior to alignment, the feature 980 isnot in contact with the z-pillar 934 b. After alignment, the device 920is moved into position to the right (+y-direction) until contact is madebetween the alignment pillar 934 b on device 912 and the alignmentfeature 980 of the device 920 to achieve alignment in the y-direction,and as the device is guided into alignment in the y-direction, thetriangular shape of the z-pillar 934 b will further assert guidance ofthe device 920 into position in the x-direction. The spacing betweendevices in FIG. 9A is denoted as “Design spacing in y-direction”. Thetop-down view in FIG. 9B(i) shows square-shaped z-pillars 934 a andtriangular-shaped z-pillars 934 b. In forming a contact with the feature980 of device 920, the z-pillar alignment aids 934 a, 934 b restrict themovement in the +x direction, the −x direction and in the +y direction.Prior to forming a contact with the device feature 980, the device 920is free to move in the +y and −y directions within the spacing betweenthe z-pillars 934 a, 934 b and the feature 980. In embodiments, apreferred location is commonly identified for optimal signal transferbetween the optical devices 912, 920 and a lateral constraint design isimplemented that enables the movement to this preferred position. InFIG. 9B(ii), for example, a preferred design spacing is shown withlateral spacing between devices as indicated by the “design spacing iny-direction.” The spacing shown is achieved in the embodiment as aresult of the contact that is formed between the long edges of thetriangular z-pillars 934 b and the long edges of the device feature 980of device 920 that form a contact with the z-pillars 934 b as shown inFIG. 9B(i). The lateral constraints are labeled in the FIG. 9B(i) as“lateral constraint in the +/−x & +y-directions” in the top-down view inFIG. 9B(i). The lithographic level precision resulting from theco-formation of the waveguides 944, the z-pillars 934 a, 934 b shown inFIG. 9B, and the fiducial 914 yields lithographic level precision in theachievable positioning of the mounted device 920 on the device 912 andthe subsequent alignment of the optical axes and spacing of the opticaldevices 912, 920. In summary, the effective alignment of the two opticaldevices 912, 920 for optimal signal transfer, for example, requiresalignment of the horizontal axes 907 a, 907 b of the two devices 912,920, the vertical axes 908 a, 908 b of the two devices 912, 920, and thespacing between the two device 912, 920. The lateral constraint featureof the z-pillar alignment aids provides a structure and method forachieving such alignment.

It should be noted that the use of the z-pillar alignment aids 934 foralignment of the devices 912, 920 in the z-direction is typicallyunaffected by the addition of the lateral constraint features of thez-pillars 934 a, 934 b shown in FIG. 9B. The alignment of the horizontalaxes of the optical signal planes are determined in embodiments by thevertical heights of the optical axes of the devices 912, 920. The heightof the optical device 920 is determined in the embodiment shown in FIG.9B by the mechanical feature of the device 920 labeled with referenceplane 926ref that forms a contact with the top surface of the z-pillar934 a, 934 b at the reference plane 925ref. This surface to surfacecontact provides a high level of accuracy in the ultimate verticalposition of the device 920, and subsequently to the alignment of theoptical axis 907 b of this device 920 with the optical axis 907 a of thedevice 912.

Upon positioning of the body of the device 920 between and over thez-pillars 934 a, 934 b, the device 920 is positioned vertically ascontact is formed between the top of the z-pillars 934 a, 934 b and themechanical feature at the reference plane 926ref of device 920. Uponpositioning, the movement of device 920 is constrained in the +x and −xdirections as determined by the spacing between the z-pillars in thex-direction and by the width of the portion of the device 920 thatresides between the z-pillars. Furthermore, upon placement, the device920 is free to move within a narrow range in the +y and −y directionsbut is ultimately guided into position in the +y-direction as shownusing techniques further described herein until reaching a constrainedposition as determined by the requirements of the aligned devices.Guided movement in the +y-direction further guides the device 920 intoalignment in the +x-direction and in the −x-direction until the ultimateposition of the device 920 is established with a high level ofprecision. In the embodiment shown in FIG. 9B, the transfer of theoptical signal 970 is not limited by the lateral positioning of thedevice 920 relative to the waveguide 944 of device 912 as is the casewith the embodiment shown in FIG. 9A. Initial placement of the device920 into the cavity is accomplished in embodiments, using offsets, suchas offset x and offset y relative to the fiducials to establish thelocation for placing the device 920 using, for example, automated dieplacement equipment.

The fiducial 914 in cavity 949 is shown formed at the same focal plane909 as the top of the z-pillars 934 a, 934 b. Portions of the hard mask916 include the z-pillar portion 916 a and the fiducial portion 916 c.The planar waveguide portion of the hard mask 916 is removed inembodiments, as was shown in FIG. 7D. Contained within the planarwaveguide 944 is optical axis 907 a of the device 912, and this opticalaxis 907 a aligns with the optical axis 907 b as the device 920 is movedinto alignment within the cavity 948. In the embodiment shown in FIG.9B, optical device 920 may be an emitting device 920, such as a laser.In embodiments that include an emitting device, an optical signal 970will be emitted from the device 920 and be received by the planarwaveguide portion 944 that intersects the cavity 948. An optical signal970 is shown in FIG. 9B(ii).

In FIGS. 9A and 9B, two examples of embodiments for lateral constraintalignment aids 981 of PIC 902 are shown. In FIG. 9C, a number of otherexample embodiments are shown with various configuration in thequantities and shapes of the z-pillars 934 and for complementarymechanical alignment aids 980 formed on embodiments of complementaryoptical devices 920. The alignment aids shown in FIG. 9C, firstly allowspace for positioning of the optical devices 920 into a placementlocation on a PIC 902, and particularly on some embodiments, intocavities 948 formed on the PIC 902. Secondly, after positioning of theoptical device 920 onto the PIC 902, the configurations allow for theguidance of the optical devices 920 into an aligned position on the PIC902. As the optical devices 920 are guided into position over theembodiments of the z-pillars shown in FIG. 9C, the lateral movement ofthe devices are constrained to position the device 920 with a highdegree of precision. The placement of the optical devices 920 overz-pillar configurations such as those shown in FIG. 9C, enable precisealignment of optical devices when these z-pillar configurations areutilizes in alignment schemes such as those described, for example, inFIGS. 9A and 9B, among others. In FIGS. 9C(i)-9C(xii), optical features974 are shown in device body 946 with optical facet 978. In addition tothe example structures shown in FIG. 9C, other similar structures canalso be used and remain within the scope of embodiments.

In FIG. 9C(i), the configuration shown is similar to that described inFIG. 9B. The z-pillar configuration in FIG. 9C(i) includes two squareshaped pillars and two triangular shaped pillars. The triangular shapedpillars are aligned with cavities formed in the alignment feature 980 ofthe optical die 920. The shaded z-pillars 934 in FIG. 9C(i) are formed,for example, on an interposer substrate using the methods describedherein. As the device 920 is moved into position over the z-pillars 934,the optical facet 978 of the optical feature 974 of the optical device920 is moved into a constrained position in the lateral directions. Anarrow is shown to indicate the direction of movement for a mounted die920 over the shaded fixed lateral z-pillar constraints 934 shown. Alsoshown in the FIG. 9C(i) are the electrical contacts 930. The electricalcontacts play a role in the alignment process as further described inmore detail herein.

FIG. 9C(ii) to 9C(xii) show additional embodiments for z-pillar shapesand quantities. FIG. 9C are intended to demonstrate a range of shapesand features of z-pillar alignment aids and to demonstrate attributes ofthese alignment features as utilized for the purpose of providingalignment of optical devices particularly in the lateral directions. Thevertical alignment is not, in general, dependent on the shape of thez-pillars 934 in embodiments. The alignment features shown in FIG. 9Care not intended to limit the scope of embodiments. Key attributes forthe z-pillar alignment features include those detailed in thedescriptions of FIGS. 9A and 9B. In each of the embodiments shown inFIG. 9C, the complementary shapes of the z-pillars 934 of the interposerdevice structure and the alignment aids 980 of a mounted device 920provide lateral guidance in both the x and y directions as shown in thereference coordinate system in the upper left hand corner of FIG. 9C andas consistent with the reference coordinates shown in FIGS. 9A and 9B.The lateral guidance in the embodiments shown in FIG. 9C is such to forman aligned optical axis between the device 920 and another device towhich the optical axis of the device 920 is to be aligned.

Referring to FIGS. 10A-10C, FIGS. 11A-11C, and FIGS. 12A-12F, additionaldrawings are provided that illustrate additional details of embodiments.In particular, these figures show additional details of examples ofembodiments of alignment aids formed on interposer structures and oncomplementary optical die that are utilized in embodiments with thealignment aids.

In FIG. 10A(i), a perspective drawing is shown of an embodiment of anoptical device 1020 with mechanical alignment features 1080. Themechanical alignment features 1080 and the body 1046 of the opticaldevice 1020 are formed on device substrate 1060. The emitting orreceiving facet 1078 of the optical device 1020 is also shown. In FIG.10A(ii), a portion of an interposer 1004 is shown with alignment pillars1034. In some embodiments, the portion of the interposer 1004 is aportion of a PIC 1002 that is contained within a cavity (e.g, 948). Theconfiguration and arrangement of the z-pillars 1034 are complementary tothe mechanical alignment features 1080 of the optical device 1020. Inthe embodiment in FIG. 10A(iii), the optical device 1080 shown in FIG.10A(i) is shown mounted in position onto the portion of the interposer1004 that is shown in FIG. 10A(ii). In FIG. 10A(iii), the hidden andunhidden outlines of the three-dimensional structure of the opticaldevice 1020 are shown with dotted lines, and the unhidden outline of thethree-dimensional structure of the portion of the interposer 1004 withz-pillars 1034 to which the device 1020 is mounted is shown with solidlines. Hidden lines for the interposer 1004 and z-pillars 1034 are notshown, although the substrate 1060 of the optical device is showntransparent for clarity. The z-pillars 1034 are shown in recesses formedin the body 1046 of the optical device 1020. In the aligned positionshown in FIG. 10A(iii) for device 1020, the z-pillars 1034 are shown incontact with a portion of a mechanical alignment aids 1080, and portionsof the body 1046 of the optical device 1020. Additional detail on thealignment of the optical device 1020 on the interposer 1004 is shown inFIG. 10B.

In FIG. 10B(i), a top-down view of the optical device 1020 is shown, forexample, after placement in cavity 1048 of a portion of an interposerthat is used in the formation of a PIC. A portion of a planar waveguide1044 is shown intersecting the wall of the cavity 1048. Spatialclearance is shown around the z-pillars 1034 to allow for the placementof the device 1020 over the z-pillars 1034 as shown. Facets 1052, 1078of the planar waveguide 1044 and the optical device 1020, respectively,are shown. Referring to FIG. 10B(ii), the device 1020 is shown movedinto an aligned position within the cavity 1048 (in the direction of thelarge arrow) and in a position for which the facets 1052, 1078 of theplanar waveguides 1044 and the optical device 1020, respectively, are insubstantial alignment. The right edge of the placement position is shownfor reference with dotted lines. The z-pillars 1034 are fixed to thesubstrate and do not move as the optical device 1020 is moved into thealigned position. The noted “WG-to-device 1020 spacing” is limited inthe embodiment shown by the surface contact formed between the z-pillars1034 and either the mechanical alignment aids 1080, the body 1046 of thedevice 1020, or both, as shown. With the optical facets 1052, 1074 inclose proximity, the optical signals can be transferred with low signalloss between the optical feature 1074 of the optical device 1020 and theplanar waveguide 1044.

Referring to FIGS. 11A-11C, an additional embodiment is shown with adifferent arrangement of z-pillars 1134 and complementary mechanicalalignment aids 1180 from that shown in FIG. 10 . In FIG. 11A(i), aperspective drawing is shown of an embodiment of an optical device 1120with mechanical alignment features 1180. The mechanical alignmentfeatures 1180 and the body 1146 of the optical device 1120 are formed ondevice substrate 1160. The emitting or receiving facet 1178 of theoptical device 1120 is also shown. In FIG. 11A(ii), a portion of aninterposer 1104 is shown with alignment pillars 1134. In someembodiments, the portion of the interposer 1104 is a portion of a PIC1102 that is contained within a cavity (e.g, 948). The configuration andarrangement of the z-pillars 1134 are fence-like in this embodiment andcomplementary to the mechanical alignment features 1180 of the opticaldevice 1120 shown in FIG. 11A(i). In the embodiment shown in FIG.11A(iii), the optical device 1120 in FIG. 11A(i) is shown mounted inposition onto the portion of the interposer 1104 that is shown in FIG.11A(ii). In FIG. 11A(iii), the hidden and unhidden outlines of thethree-dimensional structure of the optical device 1120 are shown withdotted lines, and the unhidden outline of the three-dimensionalstructure of the portion of the interposer 1104 with z-pillars 1134 towhich the device 1120 is mounted is shown with solid lines. Hidden linesfor the interposer 1104 and z-pillars 1134 are not shown, although thesubstrate 1160 of the optical device is shown transparent for clarity.The fence-like z-pillars 1134 are shown in position in FIG. 11A(iii)alongside the mechanical alignment feature 1180 of the optical device1120. In the aligned position shown in FIG. 11A(iii) for device 1120,the z-pillars 1134 are not shown in contact with a portion of amechanical alignment aids 1180, or with portions of the body 1146 of theoptical device 1120. Additional detail on the alignment of the opticaldevice 1120 on the interposer 1104 is shown in the embodiment in FIG.11B.

In FIG. 11B(i), a top down view of the optical device 1120 is shownafter placement in cavity 1148 of a portion of an interposer that isused in the formation of a PIC. A portion of a planar waveguide 1144 isshown intersecting the cavity wall. Spatial clearance is shown betweenthe z-pillars 1134 and the mechanical alignment aids 1180 of the device1120 to allow for the placement of the device 1120 between the z-pillars1134 as shown. Facets 1152, 1178 of the planar waveguide 1144 and theoptical device 1120, respectively, are shown. Referring to FIG. 11B(ii),the device 1120 is shown moved into position within the cavity 1148 (inthe direction of the large arrow) and in a position for which the facets1152, 1178 of the planar waveguide 1144 and the optical device 1120,respectively, are in substantial alignment. The right edge of theplacement position is shown for reference with dotted lines. Thez-pillars 1134 are fixed to the substrate and do not move as the opticaldevice 1120 is moved into position. The noted “WG-to-device 1120spacing” is limited in the embodiment shown by the surface contactformed between a portion of the optical device 1120 and the wall of thecavity 1148. Allowing the device 1120 to contact the wall, in someembodiments, provides the minimum clearance between the optical facets1152, 1178 of the optical device 1120 and the planar waveguide 1144,respectively. With the optical facets 1152, 1174 in close proximity, theoptical signals can be transferred with low signal loss between theoptical feature 1174 of the optical device 1120 and the planar waveguide1144. In FIG. 11C, the device 1120 is shown in aligned position incavity 1148 of interposer 1104. A portion of the planar waveguide 1144that intersects the wall of the cavity 1148 with facet 1178 is shown insubstantial alignment with the optical facet 1152 of the optical device1120.

Referring to FIGS. 12A-12F, an example of an embodiment is shown withyet another different arrangement of z-pillars and complementarymechanical alignment aids from that shown in FIG. 10 and FIG. 11 .Additional aspects of embodiments are also described. In FIG. 12A(i), aperspective drawing is shown of an embodiment of an optical device 1220with mechanical alignment features 1280. The mechanical alignmentfeatures 1280 and the body 1266 of the optical device 1220 are formed ondevice substrate 1260. The emitting or receiving facet 1278 of theoptical device 1220 is also shown. In FIG. 12A(ii), a portion of aninterposer 1204 is shown with alignment pillars 1234. In someembodiments, the portion of the interposer 1204 is a portion of a PICthat is contained within a cavity (e.g, 948). The z-pillars 1234 areconfigured in the embodiment with two rectangle shaped pillars 1234 a(when viewed from top down) and two triangle shaped pillars 1234 b (alsowhen viewed from top down). These pillars are arranged as shown in FIG.12A(ii) to receive the complementary shaped mechanical alignmentfeatures 1280 of the optical device 1220 shown in FIG. 12A(i). In FIG.12A(iii), the optical device 1220 in FIG. 12A(i) is shown mounted inposition onto the portion of the interposer 1204 that is shown in FIG.12A(ii). In FIG. 12A(iii), the hidden and unhidden outlines of thethree-dimensional structure of the optical device 1220 are shown withdotted lines, and the unhidden outline of the three-dimensionalstructure of the portion of the interposer 1204 with z-pillars 1234 a,1234 b to which the device 1220 is mounted is shown with solid lines.Hidden lines for the interposer 1204 and z-pillars 1234 are not shown,although the substrate 1260 of the optical device is shown transparentfor clarity. The top of the z-pillars 1234 a, 1234 b form a contact withthe substrate 1260 of the device 1220. The triangular z-pillars 1234 bare aligned with a triangular cavity in the mechanical alignment feature1280 and the rectangular z-pillars 1234 a are shown in position in FIG.12A(iii) alongside a straight section of the mechanical alignmentfeature 1280 of the optical device 1220. In the aligned position shownin FIG. 12A(iii) for device 1220, the z-pillars 1234 are shown incontact with a portion of a mechanical alignment aids 1280 of theoptical device 1220. Additional detail on the alignment of the opticaldevice 1220 on the interposer 1204 is shown in the embodiment in FIG.12B.

In FIG. 12B(i), a top down view of an embodiment of the optical device1220 is shown after placement in cavity 1268 of a portion of aninterposer that is used in the formation of a PIC. A portion of a planarwaveguide 1264 is shown intersecting the cavity wall. Spatial clearanceis shown between the z-pillars 1234 a, 1234 b and the mechanicalalignment aids 1280 of the device 1220 to allow for the placement of thedevice 1220 as shown. Facets 1252, 1278 of the planar waveguide 1264 andthe optical device 1220, respectively, are shown. Referring to FIG.12B(ii), the device 1220 is shown moved into position within the cavity1268 (in the direction of the large arrow) and in a position for whichthe facets 1252, 1278 of the planar waveguides 1244 and the opticaldevice 1220, respectively, are in substantial alignment. The right edgeof the placement position with label “1220 (at placement)” is shown forreference with dotted lines. The z-pillars 1234 a, 1234 b are fixed tothe substrate and do not move as the optical device 1220 is moved intoposition. The noted “WG-to-facet 1220 spacing” is limited in theembodiment shown by the surface contact formed between the triangularz-pillars 1234 b and the corresponding inside surface of the triangularcavity in the mechanical alignment feature 1280. This contact betweenthe triangular z-pillar 1234 b and the feature 1280 sets the minimumdistance that can be achieved between the optical facets 1252, 1278 ofthe optical devices 1220 and the planar waveguide 1244, respectively.With the optical facets 1252, 1274 in close proximity, the opticalsignals can be transferred with low signal loss between the opticalfeature 1274 of the optical device 1220 and the planar waveguide 1244.

In FIG. 12C, the device 1220 is shown in aligned position in cavity 1248of interposer 1204. A portion of the planar waveguide 1244 thatintersects the wall of the cavity 1248 with facet 1278 is shown insubstantial alignment with the optical facet 1252 of the optical device1220. FIG. 12C shows an embodiment of a single optical device 1220 thatis positioned into a cavity 1248 that has a capacity of a singlediscrete device. In other embodiments, more than one discrete opticaldevice 1220 is positioned into a cavity with a capacity to hold morethan one device 1220. In yet other embodiments, the optical device 1220is an array of two or more devices that can be positioned into cavitiesthat have a capacity of more than one device 1220. FIGS. 12D-12F showdrawings of these and related embodiments in more detail.

In FIG. 12D(i), a discrete optical device 1220 is shown with featuressimilar to those described in FIG. 12A(i). In FIG. 12D(ii), a cavity1248 is shown with a capacity of four optical devices 1220 and thatcontains z-pillars 1234 a, 1234 b that are complementary to themechanical alignment features 1280 of the optical device 1220 shown inFIG. 12D(i). The cavity 1248 in FIG. 12D(ii) shows portions of fourplanar waveguides 1244 with optical facets 1252 intersecting the wall ofthe cavity 1248. In FIG. 12D(iii), four discrete devices 1220 are shownpositioned in the cavity 1248 in position over the z-pillars 1234 a,1234 b and the facets 1278 of which are aligned with the facets 1252 ofthe planar waveguides 1244.

In FIG. 12E(i), optical device 1220quad is a quad device that includesfour devices 1220 formed on a single substrate 1260. Quad devices suchas optical device 1220quad shown in FIG. 12E(i) enable more efficientfabrication with the placement and alignment of optical devices ontoPICs. Each of the four devices 1220 on the quad substrate shown is afunctional device with features similar to those described in FIG.12A(i). In FIG. 12E(ii), a cavity 1248 is shown with a capacity of onequad device 1220quad (or four discrete optical devices 1220) and thatcontains z-pillars 1234 a,1234 b that are complementary to themechanical alignment features 1280 of the optical device 1220 shown inFIG. 12E(i). FIG. 12E(ii) shows portions of four planar waveguides 1244with optical facets 1252 intersecting the wall of the cavity 1248. InFIG. 12E(iii), the quad device 1220quad is shown positioned in thecavity 1248 in position over the z-pillars 1234 a,1234 b and the facets1278 of which are aligned with the facets 1252 of the planar waveguides1244. In the embodiment shown in FIG. 12E, four optical devices 1220were included on the optical device 1220quad. In other embodiments, twooptical devices 1220 are included on a substrate 1260 and placed into acavity 1248 that has a capacity for mounting two optical devices 1220.In yet other embodiments in which two optical devices 1220 are includedon a common substrate 1260, these devices are positioned in a cavity1248 that has a capacity for a multiple of two devices 1220 including acavity 1248 that has a capacity for four devices, six devices, eightdevices, or any other multiple of two devices. In other embodiments,three optical devices 1220 are included on a substrate 1260 and placedinto a cavity 1248 that has a capacity for mounting three opticaldevices 1220. In yet other embodiments in which three optical devices1220 are included on a common substrate 1260, these devices arepositioned in a cavity 1248 that has a capacity for a multiple of threedevices 1220 including a cavity 1248 that has a capacity for sixdevices, nine devices, twelve devices, or any other multiple of threedevices. In yet other embodiments, four optical devices 1220 areincluded on a substrate 1260 and placed into a cavity 1248 that has acapacity for mounting four optical devices 1220. In yet otherembodiments in which four optical devices 1220 are included on a commonsubstrate 1260, these devices are positioned in a cavity 1248 that has acapacity for a multiple of four devices 1220 including a cavity 1248that has a capacity for eight devices, twelve devices, sixteen devices,or any other multiple of four devices. In yet other embodiments, one ormore optical devices are included on a substrate 1260 and placed into acavity 1248 that has a capacity for multiple devices 1220 and to fullyor partially fill the cavity 1248 with the one or more devices. Anexample embodiment includes a single device formed on a first substratein combination with two devices formed on a second substrate that areplaced in a cavity with a capacity for three devices. Another exampleembodiment includes a single device formed in a first substrate incombination with three devices formed on a second substrate that areplaced in a cavity with a capacity for four devices, Other exampleembodiments include other quantities of optical devices formed on afirst substrate with the same or another quantity of optical devicesformed one or more additional substrates to fully or partially fill thecavity on the substrate. In general, in preferred embodiments, theoptical device capacity of a cavity matches the number of devices in thecavity.

Referring to FIG. 12F, an embodiment of a quad device 1220quad is shownthat has a simplified alignment feature structure in comparison to theoptical device 1220quad shown in FIG. 12E. In the embodiment of thedevice 1220quad shown in FIG. 12F, two sets of z-pillars 1234 a,1234 bare provided on the substrate of the quad device as shown in FIG. 12F.In other embodiments, more than two sets of z-pillars are provided onthe quad die. In other embodiments, the z-pillars 1234 a, 1234 b can beprovided on a substrate with two optical devices, three optical devices,four optical devices, or any number of optical devices.

In FIG. 12 , the examples of embodiments shown are not intended torestrict the scope of embodiments, but rather are intended to illustratefeatures that are applicable to a wider range and scope of embodiments.

Referring to FIG. 13A-13C, the process flows for forming z-pillars 1334at one or more heights within the interposer structure are described.

Referring to FIG. 13A, a sequence of schematic drawings is shown thatillustrate an embodiment of a process flow for forming z-pillars at asingle height within an interposer structure. In Step 1 of FIG. 13A, aninterposer base structure 1301 is formed. Interposer base structure 1301may include an optional electrical interconnect layer. In Step 2 of FIG.13A, a planar waveguide layer 1305 is formed on the base structure 1301.In Step 3 of FIG. 13A, a first patterned hard mask 1316-1 is formed onthe planar waveguide layer 1305 that includes the pattern required for afirst height z-pillar. In Step 4 of FIG. 13A, a first dielectric layer1338 a is formed over the patterned hard mask 1316-1 and optionallyplanarized. In Step 5, a second patterned hard mask 1316-cavity isformed on the first dielectric layer 1338 a. In embodiments, hard mask1316-cavity is a hard mask patterned for the formation of a cavity incontrast to the numerical hard mask layer designation, such as 1316-1,for which the value ‘1’ corresponds to a 1^(st) z-pillar height. In Step6 of FIG. 13A, the dielectric layer 1338 a is etched with a selectiveprocess for removal of the dielectric material in the unmasked portionsof the layer 1338 a and the planar waveguide layer 1305 with little orno etching of the patterned hard masks 1316-1, 1316-cavity to form thez-pillars. In the embodiments shown in FIG. 13A, the z-pillars areformed at a single height. In embodiments, the depth of the etch canextend below the planar waveguide layer 1305.

Referring to FIG. 13B, a sequence of drawings is shown that illustratean embodiment of a process flow for forming z-pillars with two differentheights in an interposer structure. In Step 1 of FIG. 13B, an interposerbase structure 1301 is formed. Interposer base structure 1301 mayinclude an optional electrical interconnect layer. In Step 2 of FIG.13B, a planar waveguide layer 1305 is formed on the base structure 1301.In Step 3 of FIG. 13B, a first patterned hard mask 1316-1 is formed onthe planar waveguide layer 1305 that includes the pattern required for afirst height z-pillar. In Step 4 of FIG. 13B, a first dielectric layer1338 a is formed over the patterned hard mask 1316-1 and optionallyplanarized. In Step 5 of FIG. 13B, a second patterned hard mask 1316-2is formed on the first dielectric layer 1338 a that includes the patternrequired for a second height z-pillar. In Step 6 of FIG. 13B, a seconddielectric layer 1338 b is formed over the patterned hard mask 1316-2and optionally planarized. In Step 7 of FIG. 13B, a third patterned hardmask 1316-cavity is formed on the second dielectric layer 1338 b thatincludes the pattern required for the formation of a cavity 1348 in aportion of the dielectric layers 1338 a, 1338 b. And in Step 8 of FIG.13B, the dielectric layers 1338 b,1338 a and the planar waveguide layer1305 are etched with a selective process for removing the dielectricmaterial in the layers with a high selectivity etch process with a lowor no etch rate for the patterned hard masks 1316-1, 1316-2, 1316-cavityto form the z-pillars. In the embodiment shown in FIG. 13B, thez-pillars are formed at two heights as shown in the cavity 1348 in Step8 of FIG. 13B. In embodiments, hard mask 1316-cavity is a hard maskpatterned for the formation of a cavity 1348 in contrast to thenumerical hard mask layer designation, such as 1316-1, 1316-2 for whichthe values ‘1’ and ‘2’ correspond to a 1^(st) z-pillar height and a2^(nd) pillar height, respectively.

Referring to FIG. 13C, a sequence of drawings is shown that illustratean embodiment of a process flow for forming three or more heights ofz-pillars on an interposer substrate. In Step 1 of FIG. 13C, aninterposer base structure 1301 is formed. Interposer base structure 1301may include an optional electrical interconnect layer. In Step 2 of FIG.13C, a planar waveguide layer 1305 is formed on the base structure 1301.In Step 3 of FIG. 13C, a first patterned hard mask 1316-1 is formed onthe planar waveguide layer 1305 that includes the pattern required for afirst height z-pillar, and a first dielectric layer 1338 a is formedover the patterned hard mask 1316-1 and optionally planarized. In Step 4of FIG. 13C, a second patterned hard mask 1316-2 is formed on the firstdielectric layer 1338 a that includes the pattern required for a secondheight z-pillar, and a second dielectric layer 1338 b is formed over thepatterned hard mask 1316-2 and optionally planarized. In Step 5 of FIG.13C, a third patterned hard mask 1316-3 is formed on the seconddielectric layer 1338 a that includes the pattern required for a thirdheight z-pillar, and a third dielectric layer 1338 c is formed over thepatterned hard mask 1316-3 and optionally planarized. In Step 6 of FIG.13C, none, one, or more than one additional patterned hard masks areformed on the third dielectric layer 1338 c that includes the patternrequired for any additional z-pillars, and additional dielectric layersthat are formed over these patterned hard masks and optionallyplanarized.

In embodiments in which no additional z-pillar heights are required, afourth patterned hard mask 1316-cavity is formed on the third dielectriclayer 1338 c that includes the pattern required for the formation of acavity in a portion of the dielectric layers 1338 a, 1338 b, 1338 c. Inthese embodiments, in Step 8 of FIG. 13C, the dielectric layers 1338c,1338 b,1338 a and the planar waveguide layer 1305 are etched with aselective process for removing the dielectric material in the layerswith little or no etching of the patterned hard masks 1316-1, 1316-2,1316-3, 1316-cavity to form the z-pillars. In this embodiment, z-pillarsare formed at three heights in cavity 1348.

In embodiments in which one additional z-pillar height is required, fora total of four z-pillar heights, a fourth patterned hard mask 1316-n,with n=4, is formed on the third dielectric layer 1338 c that includesthe pattern required for a fourth height z-pillar, and a fourthdielectric layer 1338 d is formed over the patterned hard mask 1316-4and optionally planarized. In these embodiments in which a fourthz-pillar height is formed, after forming the fourth patterned hard maskfor the fourth height z-pillar, and after depositing and optionallyplanarizing a fourth dielectric layer 1338 d, a fifth patterned hardmask 1316-cavity is formed on the fourth dielectric layer 1338 d thatincludes the pattern required for the formation of a cavity in a portionof the dielectric layers 1338 a, 1338 b, 1338 c, 1338 d. In theseembodiments, in Step 8 of FIG. 13C, the dielectric layers 1338 d,1338c,1338 b,1338 a and the planar waveguide layer 1305 are etched with aselective process for removing the dielectric material in the layerswith little or no etching of the patterned hard masks 1316-1, 1316-2,1316-3, 1316-4, 1316-cavity to form the z-pillars at the four heights.

And in embodiments in which more than one additional z-pillar height isrequired, for a total of more than four z-pillar heights, an nthpatterned hard mask 1316-n, where n is the number of z-pillar hard masklayers, is formed on the (n−1)th dielectric layer that includes thepattern required for a nth height z-pillar, and an nth dielectric layeris formed over the patterned hard mask 1316-n and optionally planarized.In these embodiments in which the more than four z-pillar heights arerequired, after forming the nth patterned hard mask for the nth heightz-pillar, and after depositing and optionally planarizing an nthdielectric layer, an (n+1)th patterned hard mask 1316-cavity is formedon the nth dielectric layer that includes the pattern required for theformation of a cavity in a portion of the underlying dielectric layers.In these embodiments, in Step 8 of FIG. 13C, the dielectric layers andthe planar waveguide layer 1305 are etched with a selective process forremoving the dielectric material in the layers with a low rate ofremoval of the patterned hard masks 1316-1 to 1316-n to form themultiple height z-pillars. As the thickness of the dielectric materialincreases with increasing layers, the rate of the extent of the removalof the hard mask can become significant.

In some embodiments, the z-pillars need not be positioned within acavity. In these embodiments, a hard mask can be formed such that theresulting z-pillars are not formed in a cavity 1348. In FIG. 13D, asequence of drawings is shown that illustrate an embodiment of a processflow for forming z-pillars at a single height on an interposer without acavity. In Step 1 of FIG. 13D, an interposer base structure 1301 isformed. Interposer base structure may include an optional electricalinterconnect layer. In Step 2 of FIG. 13D, a planar waveguide layer 1305is formed on the base structure 1301. In Step 3 of FIG. 13D, a firstpatterned hard mask 1316-1 is formed on the planar waveguide layer 1305that includes the pattern required for a first height z-pillar. In Step4 of FIG. 13D, the planar waveguide layer 1305 is etched with aselective process for removing the planar waveguide material in theunmasked portions with little or no etching of the patterned hard mask1316-1 to form the z-pillars. In the embodiment shown in FIG. 13D, thez-pillars are formed at a single height. In the embodiment shown in FIG.13D, the planar waveguide layer 1305 can include a dielectric spacerlayer, for example, above or below the core of the planar waveguidelayer, or both above and below the core of the planar waveguide layerthrough which optical signals are propagated as described herein.

Referring to FIG. 13E, an example embodiment of a PIC 1302 is shown thatutilizes z-pillar alignment aids 1334-1,1334-2,1334-3 that are formed atmultiple heights to support a mounted die 1320 on an interposer device1312. Optical device 1320 is shown supported by z-pillars that have beenformed at multiple heights. The optical axis of the optical device 1320is shown in alignment with the optical device 1312, an interposer with aburied waveguide 1344. The optical axes of the optical waveguide ofdevice 1312, a waveguide formed on the interposer from the planarwaveguide layer, and the optical axes of the optical feature 1374 of theoptical device 1320 are shown in alignment with optical axis 1307 of thePIC 1302. Four hard mask layers are shown in FIG. 13E that include thehard mask 1316-1 for the first height pillar 1334-1, the hard mask1316-2 for the second height pillar 1334-2, the hard mask 1316-3 for thethird height pillar 1334-3, and the hard mask 1316-cavity used to formthe cavities 1348, 1349 for the z-pillars and the fiducials,respectively as shown. The mounted die device 1320 is shown in contactwith the three hard mask layers at the top of each of the z-pillars. Thesame hard mask that is used in the embodiment shown to form the z-pillar1334-3 is used to pattern the fiducial 1314, and the waveguide 1344. Inthe embodiment shown in FIG. 13E, a single device 1320 is shownsupported by z-pillars of multiple heights. In other embodiments, thez-pillars formed at multiple heights are utilized to provide z-directionalignment of multiple mounted devices 1320. In other embodiments, lessthan or more than three z-pillar heights can be formed.

The embodiments shown in FIG. 13A-13E illustrate the formation of thez-pillars at one or more heights for the purpose of providing alignmentaids for mounted optical devices. FIG. 13E further shows how the use ofz-pillars at multiple heights can be utilized in support of an opticaldevice and how the support of an optical device can provide for thealignment of the optical axes of optical devices on a PIC.

In FIG. 14 , an embodiment is shown in which z-pillars, fiducials, andwaveguides are formed at multiple heights and for which multiple planarwaveguides are formed in a PIC 1402 on an interposer 1401. The schematictop-down drawing in FIG. 14 shows a portion of a PIC 1402 that containstwo waveguides 1444 a, 1444 b. As the side view in FIG. 14 shows, thetwo waveguides 1444 a, 1444 b are at different elevations on theinterposer. The optical axis 1407 a for mounted device 1420 a is alignedwith planar waveguide 1444 a formed from a first planar waveguide layer.Similarly, the optical axis 1474 for mounted device 1420 b is alignedwith the optical axis 1407 b of the planar waveguide 1444 b formed froma second planar waveguide layer. In the embodiment shown in FIG. 14 , afirst hard mask layer 1416-1 includes patterns for forming the planarwaveguides 1444 a, fiducial 1414-1, and z-pillars 1434-1 at a firstheight, and a second hard mask 1416-2 for forming the planar waveguides1444 b, fiducial 1414-2, and z-pillars 1434-2 at a second height. Use ofmultiple planar waveguides with the formation of the alignment featuresas described herein can enable stacking of photonic integrated circuitson the interposer. Fiducials 1414-1, 1414-2 are formed in cavities 1449a, 1449 b respectively. In the embodiment shown, z-pillars 1434-1,1434-2are formed in cavity 1448, patterned using mask layer 1416-cavity, uponremoval of dielectric layer 1438 and portions of the planar waveguidelayers as shown. Planar waveguide layers in embodiments are typicallyformed as blanket layers on the interposer and the planar devices suchas planar waveguides 1444 a, 1444 b are patterned from these blanketlayers. Portions of the planar waveguide layers are also present in thez-pillars and the fiducials as shown unless removed in a prior step.

Referring to FIG. 15A(i), a schematic cross-sectional view of anembodiment that includes a z-pillar alignment aid 1534, the top of whichis not in horizontal alignment with the optical axis of the verticallyaligned optical devices 1512, 1520. In this embodiment, optical device1512 is formed on substrate 1500 and includes an optical feature withoptical axis 1507 a. Optical device 1512 shown in FIG. 15A(i) is, forexample, an optical waveguide, formed on the substrate 1500. The fixedoptical axis 1507 a of the optical device 1512 is shown with offset,namely z-offset 1, from a reference plane 1527ref on the top of thesubstrate 1500. Optical axis 1507 a of device 1512 in FIG. 15A(i) isshown in alignment with the optical axis 1507 b of the optical device1520. The vertical positioning of the optical axis 1507 b of device 1520is determined by the height of pillar 1534 upon which the device 1520 ismounted and by the vertical position of a mechanical plane 1526ref ofdevice 1520 that makes contact with the top of the pillar 1534. Thereference plane 1526ref corresponds to a physical surface of device 1520as shown in FIG. 15A(i). Pillar 1534, hereinafter referred to as az-pillar 1534, is formed in cavity 1548 within substrate 1500. Areference plane 1525ref is shown in FIG. 15A(i) that corresponds to thetop of the z-pillar 1534 of the substrate 1500. In the embodiment inFIG. 15A(i), the reference plane 1525ref of the substrate 1500 is shownin alignment with the reference plane 1526ref of the device 1520, and asecond offset, namely z-offset 2, is shown between the reference planes1525ref, 1526ref and the optical axis 1507 of PIC 1502.

Referring to FIG. 15A(ii), a schematic cross-sectional view of anembodiment that includes a z-pillar alignment aid 1534, the top of whichis not in horizontal alignment with the optical axis of the verticallyaligned optical devices 1512, 1520 vertically aligned devices 1512, 1520is shown. In this embodiment, optical device 1512 is formed on substrate1500 and includes an optical feature with optical axis 1507 a. Opticaldevice 1512 shown in FIG. 15A(ii) is, for example, an optical waveguide,formed on the substrate 1500. The fixed optical axis 1507 a of theoptical device 1512 is shown with offset, namely z-offset 1, from areference plane 1527ref taken, for example in FIG. 15A(ii), between areference plane on the substrate, such as the top surface of thesubstrate 1500, and the optical device 1512. Optical axis 1507 a ofdevice 1512 in FIG. 15A(ii) is shown in alignment with the optical axis1507 b of the optical device 1520. The vertical positioning of theoptical axis 1507 b of device 1520 is determined by the height of pillar1534 upon which the device 1520 is mounted and by the vertical positionof the 1526ref plane of device 1520 that makes contact with the top ofthe pillar 1534. The reference plane 1526ref corresponds to a physicalsurface of device 1520 as shown in FIG. 15A(ii) that makes contact withthe top of the pillar 1534. Pillar 1534, hereinafter referred to as az-pillar 1534, is formed in the embodiment shown in FIG. 15A(ii) on thesubstrate 1500. A reference plane 1525ref is shown in FIG. 15A(ii) thatcorresponds to the top of the z-pillar 1534 of the substrate 1500. Inthe embodiment shown in FIG. 15A(ii), the reference planes 1525ref ofthe substrate 1500 and the reference plane 1527ref below the device 1512are shown in alignment with the reference plane 1526ref of the device1520, and a single offset, namely z offset 1, from this common referenceplane to the optical axis 1507 is utilized in the formation of the PIC1502.

The embodiments shown in FIG. 15A demonstrate the implementation ofz-pillar alignment aids for which the top of the z-pillar is not inalignment with the optical axis of the PIC. Use of z-pillar alignmentaids enable the formation of reference surfaces to which optoelectricaldie can be mounted and enable other aspects of the interposer substrateto be implemented. In addition to the vertical positioning featuresprovided by the z-pillar alignment aids, lateral features are providedin some embodiments to limit lateral movement upon placement ofoptoelectrical die onto the z-pillars. Also, metal or electrical contactpads, for example, can be positioned in proximity to the z-pillaralignment aids to which optical or optoelectrical devices can bemounted. In embodiments, for example, optical and optoelectrical devicescan be secured in place using solder to secure these devices in placeafter placement and alignment for both optical and optoelectricaldevices. In embodiments that utilize optoelectrical devices, the solderconnections would secure the devices into place and provide electricalcontact to the underlying electrical interconnect layer of theinterposer base structure. In embodiments in which optical deviceswithout an electrical feature or function, the solder connections couldbe used to secure the devices into place without the requirement forelectrical connection to the underlying electrical interconnect layer.Use of the solder connections to secure the optical and optoelectricaldevices into place in PICs is described in more detail herein.

Referring to FIG. 15B, schematic cross-sectional views of embodimentsthat include optical devices 1512, 1520 with vertically aligned opticalaxes 1507 a, 1507 b, respectively, are shown. In these embodiments,optical devices 1512 are formed on substrates 1500 and include anoptical feature with optical axis 1507 a. Optical devices 1512 shown inthe embodiments in FIG. 15B are, for example, optical devices such aslasers, optical detectors, and waveguides, among others, that aremounted on the substrate 1500. The devices 1512 shown in FIG. 15B aremounted on various configurations of z-pillars 1534 formed on thesubstrates 1500 that facilitate the alignment of the devices 1512particularly in the vertical direction, but not limited to alignment inthe vertical direction. The optical axis 1507 a of the optical devices1512 are shown in alignment with the optical axis 1507 b of the opticaldevices 1520 to form the aligned optical axis 1507 of the PIC 1502.Optical devices 1520 in the embodiments shown in FIG. 15B are alsomounted on various configurations of z-pillars 1534. The optical axes1507 of the PIC 1502 are shown in the various configurations of FIG. 15Bwith an offset to the top of one or more z-pillars 1534 formed on thesubstrates 1500. In FIG. 15B(i), each of the z-pillars 1534 for opticaldevices 1512, 1520 that are formed on the substrate 1500 are formed witha common offset between the top of the z-pillar 1534 and the opticalaxis 1507 of the PIC 1502. The common offset in the embodiment in FIG.15B(i) results from the common z-pillar height of this embodiment. Inthe embodiment shown in FIG. 15B(ii), the z-pillars 1534 a for opticaldevices 1512 are formed with an offset (z-offset 1) between the top ofthe z-pillar 1534 a and the PIC optical axis 1507 that differs from theoffset (z-offset 2) between the top of the z-pillars 1534 b of theoptical device 1520 and the PIC optical axis 1507. The different offsetsbetween the optical axis 1507 and the tops of the z-pillars 1534 a, 1534b result from the different z-pillar heights that are used for the twodevices 1512,1520 shown in FIG. 15B(ii). In the embodiment shown in FIG.15B(iii), z-pillars 1534 a,1534 b for optical device 1512 and opticaldevice 1520 are formed both with an offset, z-offset 1, and an offset,z-offset 2, between the tops of the z-pillar 1534 a,1534 b and the PICoptical axis 1507. In the embodiment shown in FIG. 15B(iii), the twodifferent offsets that are shown result from the use of the two z-pillarheights for support within each of the two optical devices 1512,1520. Inother embodiments, more than two offsets between the tops of the pillars1534 and the optical axis of the PIC may be used if additional z-pillarheights are utilized within a device mounting scheme. In the embodimentshown in FIG. 15B(iv), z-pillars 1534 a for optical device 1512 areformed both with a single offset, z-offset 1, between the tops of thez-pillar 1534 a and the PIC optical axis 1507 and the optical device1520 is formed both with an offset, z-offset 1, and an offset, z-offset2, between the tops of the z-pillar 1534 a, 1534 b and the PIC opticalaxis 1507. In FIGS. 15B(i)-15B(iv), reference plane 1525ref is shown atthe top of the z-pillar 1534 with the smallest offset to the PIC opticalaxis 1507.

Referring to FIG. 15C, schematic cross-sectional views of additionalembodiments that include devices 1512, 1520 with vertically alignedoptical axes 1507 a, 1507 b, respectively, are shown. In theseembodiments, optical devices 1512 are formed on substrates 1500 andincludes an optical feature with optical axis 1507 a. Optical devices1512 shown in the embodiments in FIG. 15C are, for example, opticaldevices such as lasers, optical detectors, and waveguides, among others,that are mounted on a substrate 1500. The devices 1512 shown in FIG. 15Care mounted on various configurations of z-pillars 1534 formed incavities 1548 in the substrates 1500 that facilitate the alignment ofthe devices 1512 particularly in the vertical direction, but not limitedto alignment in the vertical direction. The optical axis 1507 a of theoptical devices 1512 are shown in alignment with the optical axis 1507 bof the optical devices 1520 to form the optical axis 1507 of the PIC1502. Optical devices 1520 in the embodiments shown in FIG. 15C are alsomounted on various configurations of z-pillars 1534. The optical axes1507 of the PIC 1502 are shown in the various configurations of FIG. 15Cwith an offset to the top of one or more z-pillars 1534 formed in thecavities 1548 in the substrates 1500. In the embodiment shown in FIG.15C(i), z-pillars 1534 for optical devices 1512, 1520 are shown and eachof the z-pillars is formed in a cavity 1548 in the substrate 1500. Thez-pillars 1534 are formed with a common offset, namely z-offset 1,between the top of the z-pillar 1534 and the optical axis 1507 of thePIC 1502. Similarly, in the embodiment shown in FIG. 15C(ii), z-pillars1534 for optical devices 1512,1520 are also shown for which each of thez-pillars 1534 is formed in a cavity 1548 in the substrate 1500, and forwhich the z-pillars 1534 are formed with a common offset, namelyz-offset 1, between the top of the z-pillar 1534 and the optical axis1507 of the PIC 1502. In the embodiment shown in FIG. 15C(ii), a thirdoptical device, a waveguide 1544, is formed on the substrate 1500 with asecond offset, namely z-offset 2, to the reference plane 1527ref at thetop of the substrate. Optical waveguides 1544 provide a propagationpathway for optical signals that are transferred between optical devices1512, 1520 that are generally more focused and less lossy than in air,and commonly preferred for many applications in PICs. Embodiments inFIG. 15C(ii), FIG. 15C(iii), and FIG. 15C(iv) are shown with variousexample configurations with waveguides present between optical devices1512, 1520 and with various configurations of z-pillars formed incavities 1548. Cavities 1548 formed in the interposer provide uniquebenefits in the formation of PICs in that the formation and alignment ofthe waveguides 1544 and the z-pillars 1534 can provide improvedalignment integrity with reduced transmission losses between the opticaldevices 1512,1520 and between the waveguides as further describedherein. The waveguide 1544 shown in the embodiment in FIG. 15C(ii) is awaveguide that is formed on the substrate 1500. In the embodiment shownin FIG. 15C(iii), the waveguide 1544 is formed within the substrate 1500and in this embodiment, the z-pillars 1534 for optical devices 1512,1520, formed in cavities 1548, are also shown for which each of thez-pillars 1534 are formed with a common offset, namely z-offset 1,between the top of the z-pillar 1534 and the optical axis 1507 of thePIC 1502. Alternatively, in the embodiment shown in FIG. 15C(iv),waveguide 1544 is formed within the substrate 1500 and in thisembodiment, the z-pillars 1534 a for optical device 1520 are shown witha first offset, namely z-offset 1, between the top of the z-pillar 1534and the optical axis 1507 of the PIC 1502, and z-pillars 1534 b foroptical device 1512 are shown with a second offset, namely z-offset 2,between the top of the z-pillars 1534 b and the optical axis 1507 of thePIC 1502.

In embodiments, the waveguide 1544 is an optical pathway for an opticalsignal. In other embodiments, the waveguide 1544 is an optical devicesuch as an arrayed waveguide or other form of optical device. An in yetother embodiments, the waveguide 1544 is one or more waveguides andoptical devices used in the formation of the PIC 1502.

It should be noted that the various configurations of z-pillar heightsshown in FIG. 15B can also be combined with the configurations ofcavities and waveguides 1544 shown in FIG. 15C. The embodiment shown inFIG. 15C(iii) can be formed, for example, with one or more z-pillars1534 a supporting device 1512 that have a first offset between the topof the z-pillar 1534 a and the optical axis 1507 of the PIC 1502 andwith one or more z-pillars 1534 b supporting device 1512 that have asecond offset between the top of the z-pillar 1534 and the optical axis1507 of the PIC 1502. This embodiment can be compared to the non-cavitycontaining case described in the embodiment shown in FIG. 15B(iii). Inthe embodiment shown in FIG. 15B(iii), two different offsets are shown.In other embodiments, more than two offsets between the tops of thepillars 1534 and the optical axis 1507 of a PIC 1502 may be used in PICs1502 formed with cavities 1548. And in yet other embodiments, one ormore devices have a single offset between the top of the z-pillars 1534and the optical axis 1507 of the PIC 1502 and one or more devices havetwo or more offsets between the top of the z-pillars 1534 and theoptical axis 1507 of the PIC 1502. In FIGS. 15C(i)-15C(iv), referenceplane 1525ref is shown at the top of the z-pillar 1534 with the smallestoffset to the PIC optical axis 1507, and reference planes 1526ref arereference surfaces formed on the optical devices 1512, 1520 that contactthe top of the z-pillars 1534.

Referring to a FIG. 15D(i), a schematic cross-sectional view of anembodiment that includes vertically aligned devices 1512, 1520 is shownfor which the surfaces of these devices coincident with the referenceplanes 1526ref form a contact with the bottom surface of the cavity 1548in contrast with embodiments in which the contact is made at the top ofthe z-pillar 1534. Vertical alignment in embodiments such as thoseprovided in FIG. 15D(i) is determined wholly or in part by the depth ofthe cavity 1548 and the offset, namely z-offset 1, between the opticalaxis of the optical device 1512, 1520 and the contact surface of thesedevices 1512, 1520 coincident with the reference planes 1526ref. Awaveguide 1544 is shown in the embodiment in FIG. 15D(i) between thealigned devices 1512, 1520. The optical axis of the waveguide 1544 is inalignment with the optical axes 1507 a, 1507 b, respectively, of theoptical devices 1512, 1520, which are aligned with the optical axis 1507of the PIC 1502. A second offset is shown, namely z-offset 2, which isthe distance between the optical axis 1507 of the PIC 1502, and thesubstrate upon which the optical waveguide 1544 is formed.

In FIG. 15D(ii), a schematic cross-sectional view of an embodiment thatincludes vertically aligned devices 1512, 1520 is shown for which thesurfaces of these devices coincident with the reference planes 1526refform a contact with the bottom surface of the cavity 1548 in contrastwith embodiments in which the contact is made at the top of the z-pillar1534. The waveguide 1544 between the optical devices 1512, 1520 isformed within the substrate 1500. Vertical alignment in embodiments suchas those provided in FIG. 15D(ii) is determined wholly or in part by thedepth of the cavity 1548 and the offset, namely z-offset 1, between theoptical axis of the optical device 1512, 1520 and the contact surface ofthese devices 1512, 1520 coincident with the reference planes 1526ref.The waveguide 1544 shown in the embodiment in FIG. 15D(i) between thealigned devices 1512, 1520 is formed within the substrate 1500. Theoptical axis of the waveguide 1544 is in alignment with the optical axes1507 a, 1507 b, respectively, of the optical devices 1512, 1520, whichare aligned with the optical axis 1507 of the PIC 1502. A second offsetis shown, namely z-offset 2, which is the distance between the opticalaxis 1507 of the PIC 1502, and the substrate within which the opticalwaveguide 1544 is formed.

Referring to a FIG. 15E, schematic cross-sectional views of embodimentsthat includes aligned devices 1512, 1520 is shown in which an opticaldevice, namely the optical device 1512 shown in FIG. 15E, is an opticaldevice mounted at an edge formed in the substrate 1500. Optical devices,such as fiber optic cable mounting blocks, for example, are mounted atan edge formed on the substrate 1500 of a PIC 1502 to provide a means tocouple optical signals between PICs and optical cables that enabletransmission from and delivery to the PICs. Optical device 1512 is shownmounted at an edge formed on the substrate 1500 with an offset, z-offset1 between the optical axis 1507 a of device 1512 and a first referenceplane 1526ref-a, and an offset, z-offset 2 between the optical axis 1507a of device 1512 and a second reference plane 1526ref-b as shown in FIG.15E(i). The second offset, namely z-offset 2, shown in FIG. 15E(i) isoptionally included to provide, for example, improved mechanicalstability of the mounting of device 1512 on substrate 1500. The opticalaxis 1507 a of the optical device 1512 mounted at the edge of thesubstrate 1500 is shown in alignment with the optical axis 1507 b of theoptical device 1520 also mounted on the substrate 1500. The alignment ofthe optical axes 1507 a, 1507 b of the optical devices 1512, 1520facilitates the efficient transmission of optical signals between thesedevices. Optical device 1520 is shown mounted on z-pillar 1534 in cavity1548 with an offset, namely z-offset 3, between the top of the z-pillar1534 and the optical axis 1507 b. In other embodiments, the z-pillars1534 are formed without a cavity 1548 as, for example, the embodimentsshown in FIG. 15B. In yet other embodiments, the z-pillars 1534 areformed without a cavity and the one or more z-pillars are formed withone or more offsets from the optical axis 1507 of the PIC 1502. In yetother embodiments, one or more z-pillars 1534 are formed with one ormore offsets from the optical axis 1507 within a cavity 1548, such asthose shown in FIG. 15C, in combination with optical devices mounted atthe edge of the substrate 1500, such as the optical device 1512 shown inFIG. 15E(i). And in yet other embodiments, waveguides 1544 or otheroptical devices are present between the devices 1512, 1520.

Referring to FIG. 15E(ii), optical device 1512 is a fiber optic cablemounting block 1512 with mounted fiber optic cable 1554. The fiber opticcable mounting block 1512 is shown in the embodiment mounted in contactwith z-pillar 1534 and on the surfaces of the mounting block 1512coincident with the reference planes 1526ref-a, 1526ref-b of themounting block 1512. An optical fiber mounting block such as thatdepicted in the embodiments shown in FIG. 15E(ii) is a mounting blockused, for example, in PIC applications to attach a fiber optic cable toa substrate. The fiber optic cable mounting block 1512, shown in theembodiment forms a contact with z-pillar 1534 and optionally with aledge 1553 formed in the substrate 1500 to provide vertical alignment ofthe optical plane of the fiber core 1556 of the fiber optic cable 1554and the optical plane 1507 of the PIC 1502, and to provide mechanicalstability to the union of the mounting block 1512 and the substrate1500. In the embodiment shown, a projection of the z-pillar 1534 isshown (with dotted vertical lines) supporting the fiber optic cablemounting block 1512 in FIG. 15E(ii) since the z-pillars 1534 are not inthe same cross-sectional plane, in general, as the core 1556 of thefiber optic cable 1554 but rather the z-pillars 1534 are positionedoffset from the fiber optic core 1556. A single z-pillar 1534 is shownin FIG. 15E(ii). In other embodiments, two or more z-pillars 1534 arepresent to support the fiber optic cable mounting block 1512. The fiberoptic cable mounting block 1512 is shown with a portion of a fiber opticcore 1556 and the fiber cladding 1555 of the fiber optic cable 1554. Aperspective drawing of the fiber optic cable mounting block is shown inFIG. 15E(iii). The alignment of the optical axis 1507 a of the fibermounting block 1520 with the optical axis of the PIC 1502 to which thefiber optic mounting block is attached, facilitates the efficienttransmission of optical signals between the optical fiber core 1556 ofthe optical fiber cable 1554 and other components in the PIC 1502, suchas optical device 1520 as shown in FIG. 15E(i) and FIG. 15E(ii).

In the embodiments shown in FIG. 15E(ii), optical device 1512 is alignedwith the optical axis 1507 b of the optical device 1520 to form all orpart of a PIC 1502. The optical axis 1507 a is offset with z-offset 1from the mounting surface coincident with the reference plane 1526ref-aof the fiber optic cable mounting block 1512. A second offset, namelyz-offset 2, shown in FIG. 15E(ii) is optionally provided, for example,to contribute to improved mechanical stability of the mounted device1512.

FIG. 15E(iii) shows an example embodiment of a fiber optic cablemounting block 1562 such as, for example, the mounting block 1512. Themounting block 1562 has base 1564 and lid 1566. Lid 1566, in thisembodiment clamps or otherwise holds fiber optic cable 1554 to the base1564. In the embodiment shown in FIG. 15E, a portion of a fiber opticcable 1564 is shown. Fiber optic cables 1554 are used in embodiments totransfer information between modes in a fiber optic network, forexample, and the fiber optic cables, in embodiments, would be sufficientin length to transfer information a connected node or nodes.

Referring to FIG. 15E(iv), an embodiment is shown in which the z-pillar1534 supporting the fiber mounting block 1512 is formed in a cavity1548. Formation of the z-pillar 1534 in cavity 1548 allows foraccommodation of devices and alignment of devices into the depth of thesubstrate 1500. In embodiments, for example, in which device 1512, suchas the mounting block shown in FIG. 15E(iv), among others, requiresalignment with a device 1520 such as a planar waveguide, the formationof a z-pillar 1534 in the cavity 1548 enables lowering of the fiber core1556 while also enabling the co-formation of the z-pillar 1534 and theplanar waveguide core as further described herein. In FIG. 15E(iv), thedevice 1520 is a planar waveguide.

Referring to FIG. 15E(v), the embodiment shown shows the optical axis1507 a of a fiber optic cable mounting block 1512 in alignment with theoptical axis 1507 b of device 1520. In this embodiment, the z-pillars1534 of both the devices 1512, 1520 are formed in cavities 1548 allowingfor the co-formation of the z-pillars 1534 a and 1534 b at the sameheight, or for the formation of z-pillars 1534 a, 1534 b at differentheights as shown.

Referring to FIG. 15F, embodiments are shown in which two opticaldevices are shown with aligned optical signal planes 1507 a, 1507 b.Device 1512 is, for example, a ball lens. In these embodiments, the balllens 1512 is shown in alignment with optical device 1520. Device 1520 isshown mounted on the z-pillar 1534 formed in cavity 1548. The opticalsignal plane is shown with an offset, namely z-offset as shown in thefigure, between the optical axis 1507 and the mounting reference plane1526ref of the device 1520, coincident with the reference plane 1525refat the top of the z-pillar 1534. The embodiment shown in FIG. 15F(i) isshown without a planar waveguide between the two optical devices 1512,1520 and the embodiment shown in FIG. 15F(ii) is shown with a planarwaveguide between the two optical devices 1512, 1520.

Referring to FIG. 16 , a PIC structure 1602 is shown for which thelayers used in the formation of the planar waveguide are used in theformation of a portion of the z-pillar 1634. FIG. 16 shows across-hatched portion of the device 1612 that forms the planar waveguidelayer 1644 and a similar corresponding cross-hatched layer at the sameheight in the z-pillar 1634 just below the hard mask 1616. Theco-formation of the z-pillar 1634 with the planar waveguide structure1644 provides for an improvement in the integrity of the referenceheights between the top of the z-pillar 1634 and the core of the planarwaveguide 1644. This improvement in the integrity of the alignmentbetween the top of the z-pillar 1634 and the planar waveguide occurs asa result of linking the heights of the planar waveguide and the z-pillarheights to one another and not to a structure that is formed ordependent on the height of the bottom of the cavity. Variations in thethickness of the underlying layers below the cavity upon which thez-pillars are formed are present in both the layers underlying theplanar waveguide 1644 on the base structure 1601 and the layersunderlying the cavity 1648 and are thus compensated for in a structurethat is formed using the layers up to and including the layers used inthe formation of the waveguide 1644. Also shown in FIG. 16 is theoptical feature 1674 of a mounted optical device 1620 in alignment withthe optical axis 1607 of the PIC 1602. Fiducial 1614 may be, but is notnecessarily, aligned horizontally with the optical axis 1607 in theembodiment shown in FIG. 16 and is used in embodiments as an alignmentaid for placement and alignment of devices such as mounted device 1620onto the PIC 1602.

Referring to FIG. 17 , a PIC structure 1702 is shown for which thelayers used in the formation of the planar waveguide are used in theformation of a portion of the z-pillar 1734 and in the formation of thefiducial 1714. FIG. 17 shows a cross-hatched portion of the device 1712that forms the planar waveguide layer 1744, a similar correspondingcross-hatched layer at the same height in the z-pillar 1734 just belowthe hard mask 1716, and another cross-hatched layer at the same heightin the fiducial mark 1714. The cross-hatched layer shown in FIG. 17 isformed in embodiments, for example, from the planar waveguide layer ofthe interposer. (See layer 405 for example in FIG. 4 .) The co-formationof the z-pillar 1734 and the fiducial 1714 with the planar waveguidestructure 1744 of device 1712 provides for an improvement in theintegrity of the reference heights between the top of the z-pillar 1734and the core of the planar waveguide 1744, and an increase in theplacement and alignment precision that is achievable using the fiducial1714 for lateral alignment. This improvement in the integrity of thealignment between the top of the z-pillar 1734 and the planar waveguideoccurs as a result of linking the heights of the planar waveguide andthe z-pillar heights to one another and not to a structure that isformed or dependent on the height of the bottom of the cavity.Furthermore, the improvement in the integrity of the lateral alignmentoccurs as a result of the improvement in optical resolution achievablebetween the z-pillars 1734 and the fiducials 1714 since these structuresare formed at the same height using the same hard mask layer 1716 andthus have the same focal length when viewed from above. Fiducial 1714 isformed in cavity 1749 in dielectric layer 1738 to provide opticalvisibility when view from above. Variations in the thickness of theunderlying layers below the cavity upon which the z-pillars 1734 areformed are present in both the layers underlying the planar waveguide1744 on the base structure 1701 and the layers underlying the cavity1748, as is the case in the embodiments shown in FIG. 16 , and are thuscompensated for in a structure that is formed using the layers up to andincluding the layers used in the formation of the waveguide 1744. Alsoshown in FIG. 17 is the optical feature 1774 of a mounted optical device1720 in alignment with the optical axis 1707 of the PIC 1702. Fiducial1714 is shown in horizontal alignment with the optical axis 1707 in theembodiment shown in FIG. 17 and is used in embodiments as an alignmentaid for placement and alignment of devices such as mounted device 1720,among other devices, onto the PIC 1702.

Referring to FIG. 18 , additional embodiments are shown for which thez-pillars and fiducials are formed concurrently and at the same heightin the interposer structure and other additional embodiments are alsoshown for which the z-pillars, fiducials, and planar waveguides areformed concurrently and at the same height in the interposer structureusing, for example, the planar waveguide layer 405 as shown in FIG. 4and a patterned hard mask layer such as hard mask layer 714 shown inFIG. 7D in which a portions of the hard mask 716 a,716 b, 716 c are usedto define the z-pillars 734, the planar waveguides 744, and the fiducial714, respectively, for the patterning of the planar waveguide layer 705portion of the z-pillars 734, the planar waveguides 744, and thefiducial 714.

Referring to FIG. 18A(i), an embodiment is shown for which an offset,“z-offset”, is provided between the top surface of the hard mask 1816 atthe tops of the z-pillar 1834 and fiducial 1814, and the optical axis1807 of the PIC 1802. Multiple mounted devices 1820 a, 1820 b are shownmounted on the z-pillar alignment aids 1834 in FIG. 18A(i) along withoptical device 1812, a planar waveguide, for example. The offset,“z-offset” shown in FIG. 18A(i) is largely a consequence of the finitethickness of the hard mask 1816. A mechanical reference plane 1826ref isformed on the mounted devices 1820 a, for example, and surface tosurface contact is formed between this mechanical reference plane1826ref and the top surface of the z-pillar structure 1834 at thereference plane 1825ref. Exposure of the fiducial 1814 with theformation of cavity 1849 provides optical visibility to the fiducial1814 for optical alignment equipment used in the placement of devices,for example, onto the PIC 1802. FIG. 18A(ii) shows a similar embodimentto that shown in FIG. 18A(i) with the exception that the devices 1820 a,1820 b are not placed in cavities 1848 and the fiducial is not formed ina cavity 1849.

Referring to FIG. 18B, a PIC 1802 is shown that includes a mounteddevice 1820 that is mounted on z-pillar alignment aids 1834 and a device1812 that is formed on the base structure 1801. In embodiments, thedevice 1820 may be an optical device or optoelectrical device asdescribed herein. The device 1812, in embodiments is a waveguide, alens, a grating, or other optical device that can be fabricated on thesubstrate and that incorporates within it the planar waveguide layer(such as layer 405, for example, shown in FIG. 4 .) Device 1812 may beformed from growth processes, for example, such as a chemical vapordeposition or other form of deposition process or a combination of filmformation processes. The optical axis of the PIC 1807 is shown to bealigned through the device 1812, the z-pillars 1834 that are used insupporting device 1820, and the fiducial 1814. An offset, “z-offset”isshown between the top of the hard mask 1816 at the top of the z-pillar,for example, and the optical axis 1807 of the PIC 1802. A mechanicalreference plane 1826ref is shown on the mounted devices 1820 and surfaceto surface contact is formed between this mechanical reference plane1826ref and the top surface of the z-pillar structure 1834 at thereference plane 1825ref. Fiducial 1814 is optically visible for opticalalignment equipment used in the placement of devices, for example, ontothe PIC 1802. Other embodiments within the scope of embodiments areformed such that the fiducial 1814 is formed in a cavity such as cavity1849 in FIG. 18A(i). It should be noted that although the portion of thefiducial 1814 is formed from the planar waveguide layer (hatched portionof the fiducial 1814 shown in FIG. 18B), the use of the fiducial 1814 istypically limited to that of an alignment aid, and does not, in generalfunction as an optical device or as a part of an optical device. The useof the fiducial as all or a part of an optical device is not precludedin any way in the embodiments described herein, however.

Referring to FIG. 18C, additional embodiments are shown for whichz-pillars and fiducials are formed concurrently and for which opticaldevices are mounted on the z-pillar alignment aids, and for which theoptical propagation path 1807 for the PIC 1802 is formed above theplanar waveguide layer (e.g, 405). Referring to FIGS. 18C(i) and18C(ii), PICs 1802 are shown for which an offset, “z-offset”, isprovided between the optical axes 1807 a, 1807 b of mounted opticaldevices 1812, 1820 and the top surface of the top surface of thez-pillar 1834. Z-pillar alignment aids 1834 are formed in cavities 1848that are formed in base structure 1801 in FIG. 18C(i) and withoutcavities on the base structure 1801 in 18C(ii). The offset, “z-offset”shown in FIG. 18C(i) is the distance above the top of the z-pillar 1834at which an optical signal laterally propagates between devices 1812,1820 in the embodiment shown. The optical feature of device 1820 islocated at this “z-offset” distance from the mechanical reference plane1826ref that corresponds in the figure with the mechanical feature ofthe device 1820 (or 1812) that forms a surface to surface contact withthe top of the z-pillar 1834. The horizontal plane of the opticalfeatures of the devices in FIG. 18C correspond to the horizontal opticalplane through or from which the optical signal 1807 b is generated,received, or otherwise propagated in the device 1820. This horizontalplane is formed at a distance corresponding to the “z-offset” distanceshown in FIG. 18C and determines the height at which the optical signalpropagates through the PIC. The mechanical reference plane 1826ref isformed on the mounted devices 1820 a, for example, and surface tosurface contact is formed between this mechanical reference plane1826ref and the top surface of the z-pillar structure 1834 at thereference plane 1825ref. Exposure of the fiducial 1814 with theformation of cavity 1849 provides optical visibility to the fiducial1814 for optical alignment equipment used in the placement of devices,for example, onto the PIC 1802. The common focal plane that is sharedbetween the z-pillars 1834 and the fiducial 1814 provides optimalresolution between these features during automated placement of mounteddevices such as optical devices 1812, 1820. FIG. 18C(ii) shows a similarembodiment to that shown in FIG. 18C(i) with the exception that thedevices 1812, 1820 are not placed in cavities 1848 and the fiducial isnot formed in a cavity 1849.

Referring to FIG. 18D, additional embodiments are shown for whichz-pillar alignment aids are formed at multiple heights with thefiducials formed and at the same height as one or more of the z-pillars.In the embodiments shown in FIG. 18D, the fiducials and the z-pillars atleast one of the heights are formed concurrently and at the same heightin the interposer structure using, for example, the planar waveguidelayer 405 as shown in FIG. 4 and a patterned hard mask layer such ashard mask layer 714 shown in FIG. 7D in which a portions of the hardmask 716 a,716 b, 716 c are used to define the z-pillars 734, the planarwaveguides 744, and the fiducial 714, respectively, for the patterningof the planar waveguide layer 705 portion of the z-pillars 734, theplanar waveguides 744, and the fiducial 714.

Referring to FIG. 18D(i), an embodiment is shown for which a firstoffset, “z-offset 1”, is provided between the top surface of one or morez-pillars 1834 a and the fiducial 1814, and the optical axis 1807 b ofthe PIC 1802. At least one mounted device 1820 is shown mounted on thez-pillar alignment aids 1834 a in FIG. 18D(i) with this first offset,namely “z-offset 1”. A second optical device 1812 with optical axis 1807a is mounted on one or more z-pillars 1834 b at a different height thanz-pillars 1834 a. The optical axis 1807 a of device 1812 is shown inalignment with the optical axis of device 1807 b and in alignment withthe optical axis 1807 of the PIC 1802 of FIG. 18D(i). A second offset,namely “z-offset 2” is provided between the top surface of one or morez-pillars 1834 b and the optical axis 1807 b of the PIC 1802. Amechanical reference plane 1826ref is formed on the mounted devices 1820and on device 1812, for example, and surface to surface contact isformed between this mechanical reference plane 1826ref and the topsurface of the z-pillar structure 1834 a, 1834 b. In FIG. 18D(i), thetop surface of the first z-pillar 1834 a is shown at the mechanicalreference plane 1825ref. Mechanical reference plane 1825ref is areference plane that corresponds, in the embodiment in FIG. 18D(i) withthe top of the z-pillar 1834 a. Similar embodiments to the embodimentshown in FIG. 18D(i) are also shown in FIGS. 18D(ii) and 18D(iii) whichshow other configurations of z-pillar arrangements at multiple heights,and with the corresponding z-offsets for each of the z-pillar heightsshown relative to the optical axis 1807. In FIG. 18D(ii), the z-pillaralignment aids 1834 a, 1834 b are shown at multiple heights within eachof the two aligned optical devices 1812, 1820 and in FIG. 18D(iii), thez-pillar alignment aids 1834 a are shown the same height for opticaldevice 1820 and the alignment aids 1834 a, 1834 b are shown at multipleheights for the optical device 1812. In FIGS. 18D(i)-18D(iii), theheight and structure of the z-pillar alignment aid 1834 a corresponds tothe height and structure of the fiducial 1814 in these embodiments. Anadditional feature to note in FIG. 18D is that the optical axes 1807 a,1807 b of the devices 1812, 1820 are also in alignment with the opticalaxis formed with the planar waveguide layer (layer 405, for example) inthe z-pillar 1834 a and in the fiducial 1814.

Referring to FIG. 18E, additional embodiments are shown for whichz-pillar alignment aids are formed concurrently with a fiducial, and forwhich one of the mounted devices is a lens. Lenses are commonly used inPICs to provide focus to an optical signal in a PIC. In FIG. 18E,optical device 1812 is shown as a lens, and in particular a ball lens.Three configurations are shown in FIG. 18E for a ball lens on a PIC thatuse z-pillar alignment aids 1834 in support of a mounted optical device1820, and a fiducial that is concurrently formed with one or morez-pillars 1834. In the embodiments shown in FIG. 18E(i), the fiducials1814 and the z-pillars 1834 are formed at the same height in theinterposer structure using, for example, layers that include the planarwaveguide layer 405 as shown in FIG. 4 and a patterned hard mask layersuch as hard mask layer 714 shown in FIG. 7D in which a portions of thehard mask 716 a,716 c are used to define the z-pillars 734 and thefiducial 714, respectively. In the embodiment shown in FIG. 18E(i), aplanar waveguide section is not shown but may be present on or withinanother portion of the PIC 1802. The alignment of the heights of thefiducial 1814, formed in cavity 1849, and the z-reference pillar 1834ensures that these features lie in the same focal plane for optimalresolution in placement and alignment operations that require movementsin reference to the fiducial and placement in reference to thez-pillars, for example, in embodiments.

In the embodiment in FIG. 18E(i), an offset, namely “z-offset”, isprovided between the top surface of the one or more z-pillars 1834 andthe optical axes 1807 b of the mounted optical device 1820. The opticaldevice 1820 has mechanical reference plane 1826ref that forms a surfaceto surface contact with the top of the z-pillar 1834. A second device1812 is a ball lens that is mounted in the embodiment in a recess 1837.The optical axis 1807 a of the ball lens 1812 in FIG. 18E(i) is alsooffset a distance “z-offset” from the mechanical reference plane 1825refat the top of the pillar 1834. The optical axis 1807 a of device 1812 isshown in alignment with the optical axis of device 1807 b and inalignment with the optical axis 1807 of the PIC 1802 of FIG. 18E(i).Referring to FIG. 18E(ii), an embodiment is shown that is similar to theembodiment shown in FIG. 18E(i) with the addition of a planar waveguide1844 on the base structure 1801. In this embodiment, the fiducial 1814,the z-pillar 1834, and the planar waveguide 1844 are patterned from thesame hard mask layer (See FIG. 7D, for example) and in part from thesame planar waveguide layer (see layer 405, for example, in FIG. 4 ).The optical axis of the planar waveguide layer, the cross-hatched layerin FIGS. 18E(i)-18(iii), is aligned with the optical axis 1807 a of theball lens 1812 and the optical axis 1807 b of the mounted optical device1820 as shown in FIG. 18E(ii). FIG. 18E(iii) shows a similarconfiguration to that in FIG. 18E(ii) but with a shortened planarwaveguide device 1844 between the ball lens and device 1820. Theshortened length of the planar waveguide 1844 may also be an opticaldevice such as an isolator or other optical device.

In FIGS. 18A-18E, embodiments are shown that demonstrate a range ofimplementations available with the various configurations of thealignment aids that include the z-pillars and the fiducials, and variousintegration schemes that can be implemented in embodiments for whichthese alignment aids are formed together with a planar waveguide layerof a planar waveguide-based device and in other embodiments for whichthese alignment aids are formed independently of planar waveguide-baseddevices.

Referring to FIG. 19 , an additional drawing of an embodiment isprovided that shows the portions of the planar waveguide layer (e.g,layer 405 shown in FIG. 4 ) that reside within the various alignmentaids. FIG. 19 also provides a summary of some key features of someembodiments. The planar waveguide layer is shown in FIG. 19 as thecross-hatched layer within the z-pillar 1934 and the fiducial 1914alignment aids. This layer is also present in the waveguide 1944 of theoptical device 1912. Optical device 1912 in FIG. 19 is a buriedwaveguide structure on the interposer base structure 1901. Thecross-hatched layer is formed from the same planar waveguide layer (e.g,layer 405) and patterned using the same hard mask layer in theembodiment shown in FIG. 19 . The cross-hatched portions of the z-pillar1934 and the fiducial 1914 are portions of these structures that areformed from the planar waveguide layer. Device 1920 is mounted onz-pillar 1934 and a contact is formed between the mechanical referencesurface formed on the device 1920 and the top of the z-pillar 1934 inthe embodiment shown. This surface to surface contact establishes theresulting height of the optical feature 1974 and the optical axis 1907 bof the optical device 1920. An optical feature 1974 of an optical device1920 is, for example, a laser cavity and facet for a laser or areceiving volume and facet for a photodetector. Optical feature 1974 maybe any of a number of other optical features for other optical devicesthat can be utilized in a PIC. The optical feature 1974 is typically theportion of the device 1920, 1912 through which the optical signalpropagates and is typically aligned with the optical axis 1907 b. Theoptical axis 1907 b of the device 1920 is aligned with the optical axis1907 a of the device 1912. Optical axes 1907 a, 1907 b in alignment formall or part of the optical axis 1907 of the PIC 1902. The fiducial 1914is formed in cavity 1949 using hard mask 1916-cavity at the same focalplane, in the embodiment shown, as the z-pillar 1934. A common hard mask1916 is used to pattern the planar waveguide 1944, and the z-pillar 1934and fiducial 1914 alignment aids using a process sequence as described,for example, in FIG. 7 . A lateral constraint alignment aid 1981 is alsoshown in FIG. 19 . Lateral constraint alignment aids are described indetail herein.

Referring to FIG. 20 , an additional embodiment of an additionalalignment aids that is formed using the processing methods andtechniques described herein is described. In FIG. 20(i), a cross-sectionview of a portion of a PIC structure 2002 is shown in which an opticalfiber cable 2054 is mounted in a v-groove 2050. The fiber optic cable2054 includes the core 2056 and cladding 2055. The core 2056 is alignedwith the core of a planar waveguide 2044 formed on the base structure2001. The fiducial 2014 is shown formed in cavity 2049 in dielectriclayer 2038. In FIG. 20 (ii), alignment aid 2045 is shown. Alignment aid2045 is a form of lateral constraint that is used to position the fiberoptic cable and is patterned from the planar waveguide structure 2044.The planar waveguide layers 2044 are typically deposited in a blanketlayer that can be patterned with an additional pattern required toprovide feature 2045 that surrounds one or more locations for thev-groove 2050. Use of a portion of the planar waveguide layers toidentify the location of the v-groove 2050 has a particular benefit inthe interposer structure described herein that is specific to itsintegration with other structures that utilize the planar waveguidelayers such as the planar waveguide structures 2044. The core 2056 ofthe optical fiber cable 2054, in practice, must be aligned with thewaveguide 2044 of the PIC 2002. The formation of the planar waveguides2044 and the alignment structures 2045 that are used to align theoptical fiber cable core 2056 provide a high level of precision in thefabrication of these two structures in embodiments that use the samemasking layer and process to form theses structures. In the embodimentshown in FIG. 20 , the fiducial 2014 is also shown to be formed from thesame planar waveguide layers that are used in the formation of theplanar waveguide 2044 and the v-groove alignment feature 2045.

Referring to FIG. 21 , an additional embodiment of an additionalalignment aid that is formed using the processing methods and techniquesdescribed herein is shown. In FIG. 21(i), a cross-sectional view of aportion of a PIC structure 2102 is shown in which an optical fiber cable2154 is mounted in a fiber optic cable mounting block 2162. The fiberoptic cable mounting block 2162 includes a base 2164 and a lid 2166. Inthe embodiment shown in the cross-sectional view of FIG. 21(i), aportion of the optical fiber cable 2154 is mounted in a v-groove 2150 inthe base structure 2101. In other embodiments that utilize the fiberoptic cable mounting block, the v-groove is not provided. In embodimentsthat do not include the v-groove 2150 for the fiber optic cable,alignment of the cable is provided by the alignment of the fiber opticcable block using the alignment aid described herein. Referring again toFIG. 21 that shows an embodiment that includes the v-groove 2105 and thefiber optic cable mounting block 2162, the fiber optic cable 2154 thatis mounted in the v-groove 2150 includes the core 2156 and cladding2155. The core 2156 is aligned with the core of a planar waveguide 2144formed on the base structure 2101. The fiducial 2114, shown in crosssection in FIG. 21(i) and in the top-down view of FIG. 21 (ii), isformed in cavity 2149 in dielectric layer 2138. In the top-down view inFIG. 21 (ii), alignment aid 2145 is shown with the z-pillar alignmentaids 2134 and the fiducial 2114. A projection of the z-pillar alignmentaid is shown in the cross-sectional view in FIG. 21 . Alignment aid 2145is a form of lateral constraint that is used to position the fiber opticcable mounting block 2162 that is patterned from the planar waveguidestructure 2144. The planar waveguide layers 2144 are typically depositedin a blanket layer that is patterned with an additional pattern toprovide feature 2145 surrounding one or more locations for the fibermounting block 2162. Use of a portion of the planar waveguide layers toidentify the location of the fiber mounting block 2162 has a particularbenefit in the interposer structure described herein that is specific toits integration with other structures that utilize the planar waveguidelayers such as the planar waveguide structures 2144. The core 2156 ofthe optical fiber cable 2154, in practice, must be aligned with thewaveguide 2144 of the PIC 2102. The formation of the planar waveguides2144 and the alignment structures 2145 that are used to align theoptical fiber cable mounting block 2162 provides a high level ofprecision in the fabrication and alignment of these two structures inembodiments that use the same masking layer and process to form thesestructures. The precision is provided, in embodiments, since thesepatterned features are formed using the same lithographic patterningstep. Lithographic level alignment is typically within tenths of amicron and less for the types of lithographic processes used in photonicintegrated circuits. The combination of the fiducial 2114, the z-pillar2134, and the lateral constraint alignment aid 2145 in the embodimentshown in FIG. 21 provides enhanced alignment features that are specificto the interposer structure described herein.

Referring to FIG. 22 , an additional embodiment of the alignment aidsshown in FIG. 21 for the edge mounted fiber optic cable block 2160 areshown in conjunction with the z-pillar 2234 and lateral constraintalignment aids 2281 for a mounted device 2220 on PIC 2202. In FIG.22(i), a cross-sectional view of a portion of a PIC structure 2202 isshown in which an optical fiber cable 2254 is mounted in a fiber opticcable mounting block 2262. The fiber optic cable mounting block 2262includes a base 2264 and a lid 2266. In the embodiment shown in thecross-sectional view of FIG. 22(i), a portion of the optical fiber cable2254 is mounted in a v-groove 2250 in the base structure 2201. In otherembodiments that utilize the fiber optic cable mounting block, thev-groove 2250 is not provided. In embodiments that do not include thev-groove 2250 for the fiber optic cable, alignment of the cable isprovided by the alignment of the fiber optic cable block 2262 using thealignment aid 2245 described herein or other constraining features.Referring again to FIG. 22 that shows an embodiment with the v-groove2205 and the fiber optic cable mounting block 2262, the fiber opticcable 2254 that is mounted in the v-groove 2250 includes the core 2256and cladding 2255. The core 2256 is aligned with the optical feature2274 of a mounted optical device 2220. The mounted device 2220 withoptical feature 2274 is mounted over z-pillar alignment aids 2234 formedin the cavity 2248 in the dielectric layer 2238 on base structure 2201.The fiducial 2214, shown in cross section in FIG. 22(i) and in thetop-down view of FIG. 22 (ii), is formed in cavity 2249 in dielectriclayer 2238. In the top-down view in FIG. 22 (ii), alignment aid 2245 isshown with the z-pillar alignment aids 2234 and the fiducial 2214. Aprojection of the z-pillar alignment aid 2234 that supports the fiberoptic cable mounting block 2262 is shown in the cross-sectional view inFIG. 22 . Alignment aid 2245 is a form of lateral constraint that ispatterned from the planar waveguide structure and is used to positionthe fiber optic cable mounting block 2262. The planar waveguide layersare typically deposited in a blanket layer that is patterned with anadditional pattern to provide feature 2245 surrounding one or morelocations for the fiber mounting block 2262. Planar waveguides (e.g,2144) are not shown in the embodiment in FIG. 22 but the same layersthat are used in the fabrication of the planar waveguide are used in theformation of the z-pillars 2234 and the fiducials 2214 and the alignmentaids 2245. The optical axis 2207 of the PIC 2202 is shown in alignmentfor the fiber optic cable core 2256 and the optical feature 2274 of themounted device 2220. Use of a portion of the planar waveguide layers toidentify the location of the fiber mounting block 2262 has a particularbenefit in the interposer structure described herein that is specific toits integration with other structures that utilize the planar waveguidelayers such as the z-pillar alignment aids that support the mounteddevice 2220. The core 2256 of the optical fiber cable 2254, in practice,must be aligned with the optical feature 2274 of the device 2220 that ismounted on the z-pillar alignment aids 2234. The z-pillar alignment aids2234, and particularly the z-pillar alignment aids in embodiments withlateral constraint features such as the lateral constraint feature 2281shown in FIG. 22 , used in conjunction with the alignment structures2245 that are used to align the optical fiber cable mounting block 2262,provide a high level of precision in the fabrication and alignment ofthese two structures in embodiments that use the same masking layer andprocess to form these structures. The precision is provided, inembodiments, since these patterned features are formed using the samelithographic patterning step. Lithographic level alignment is typicallywithin tenths of a micron and less for the types of lithographicprocesses used in photonic integrated circuits. The combination of thefiducial 2214, the z-pillar 2234, and the lateral constraint alignmentaid 2245 in the embodiment shown in FIG. 22 provides enhanced alignmentfeatures that are specific to the interposer structure described herein.The alignment in the z-direction, for the fiber cable mounting block2262 and hence the core 2256 of the mounted fiber optic cable 2254, canbe quite accurate since the z-pillars for the mounted device 2220 andthe fiber optic mounting block 2262 are formed using the same hard maskand film structure. Similarly, the alignment in the lateral directions,can also be quite accurate since the z-pillars 2234 portion of thelateral constraint feature 2281 for the mounted device 2220 is formedusing the same lithographic patterning step as the lateral constraintalignment features 2245.

Referring to FIGS. 23-30 , a number of process flows and process flowsequences are described for embodiments that utilize fiber optic cablemounting blocks and other alignment aids. FIGS. 23 and 24 show a processflow diagram and a sequence of drawings, respectively, that illustratethe steps in the process flow for an embodiment that utilizes a fiberoptic cable mounting block without the use of z-pillars or lateralconstraints derived from the planar waveguide layer to align the fiberoptic cable mounting block. FIGS. 25 and 26 show a process flow diagramand a sequence of drawings, respectively, that illustrate the steps inthe process flow for an embodiment that utilizes a fiber optic cablemounting block with the use of z-pillars to support the fiber opticcable mounting block. This embodiment does not use a lateral constraintalignment feature derived from the planar waveguide layer for themounting block alignment. FIGS. 27 and 28 show a process flow diagramand a sequence of drawings, respectively, that illustrate the steps inthe process flow for an embodiment that utilizes a fiber optic cablemounting block with the use of a lateral constraint alignment featurederived from the planar waveguide layer but does not use z-pillars tosupport the fiber optic cable mounting block.

Referring to FIGS. 23 and 24 , a process flow diagram and a sequence ofdrawings, respectively, are shown that illustrate the steps in theprocess flow for an embodiment that utilizes a fiber optic cablemounting block. In the embodiments described in FIGS. 23 and 24 , unlikesome other embodiments for which fiber optic cable mounting blocks areutilized, z-pillars are not used to support the fiber optic cablemounting block and additionally, the lateral constraint alignmentfeature derived from the planar waveguide layer is not used to providelateral alignment of the fiber optic cable mounting block.

Referring to FIG. 23 , a process flowchart is shown for the formation ofinterposer-based PICs with embodiments of the interposer alignmentstructures, and aspects of embodiments described in this flowchart areillustrated in FIG. 24 . In step 2390 of process flow 2310, a planarwaveguide layer 2405 is formed on a base structure, wherein the basestructure 2401 includes an optional electrical interconnect layer 2403on a substrate 2400. The planar waveguide layer 2405 on base structure2401 forms interposer 2404. The electrical interconnect layer 2403, asshown in FIG. 24A is formed in some embodiments on a semiconductorsubstrate 2400 such as silicon. Indium phosphide, gallium arsenide, orother semiconductor substrates can also be used. In yet otherembodiments, a ceramic or insulating substrate is used. In yet otherembodiments, a metal substrate is used. And in yet other embodiments, acombination of one or more semiconductor layers, insulating layers, andmetal layers are used to form a substrate 2400 upon which the optionalelectrical interconnect layer 2403 and the planar waveguide layer 2405are formed. In some embodiments, the electrical interconnect layer 2403is not in direct contact with the substrate but rather an interveninglayer is present. Similarly, the planar waveguide layer 2405, in someembodiments, is not in direct contact with the underlying electricalinterconnect layer 2403 but rather an intervening layer or layers may bepresent. In some embodiments, a semiconductor layer or substrate ismounted on a metal layer or substrate to form a composite substrate.

In hard mask layer formation step 2391 of the process flow 2310, a hardmask 2416 is formed on the planar waveguide layer 2405. Hard mask layer2416 includes patterning for the formation of the optical waveguides andall or a portion of the alignment aids that are formed from the planarwaveguide layer 2405. In the embodiments in FIG. 24B, the hard masklayer includes patterns for alignment aids that include fiducial marksand the alignment pillars or z-pillars. In the embodiments shown inFIGS. 24B, hard mask layer portion 2416 a shows a hard mask pattern foran embodiment of a z-pillar alignment aid which is shown after the hardmask patterning step in FIG. 24B; Similarly, hard mask portion 2416 bshows a hard mask pattern for an embodiment of a planar waveguide 2444which is shown after patterning in FIG. 24B. Hard mask portion 2416 cshows a hard mask pattern for an embodiment of a fiducial mark alignmentaid which is shown after hard mask patterning in FIG. 24B. In summary,in the embodiment shown in FIG. 24B, portions of the patterned hard maskinclude the z-pillar portion 2416 a, planar waveguide portion 2416 b,fiducial mark portion 2416 c. These portions of the hard mask 2416 areused to pattern the z-pillars 2434, the planar waveguides 2444, and thefiducial marks 2414, respectively, using an etch process to remove theplanar waveguide layer 2405 from areas not protected by the hard masklayer 2416 as shown in FIG. 24C.

Portions of the hard mask layer 2416, are also used in some embodimentsto form all or a portion of optical devices 2440 for embodiments inwhich the optical devices 2440 are formed wholly or in part from theplanar waveguide layer 2405. Optical devices 2440 may be waveguides,gratings, lens, or any device that can be formed from at least a portionof the planar waveguide layer. Alternatively, in other embodiments,optical devices 2440 are mounted devices, and not fabricated directlyfrom the planar waveguide layer 2405 but added at a later step in theprocess of forming the PIC 2402. Optical device 2440 can be one or moreof a portion of a device formed from the planar waveguide layer and oneor more of a portion of a mounted device.

In some embodiments, the planar waveguide layer 2405 is formed of one ormore layers of silicon dioxide, silicon nitride, and silicon oxynitrideas described herein. To pattern the planar waveguides from such layersusing a dry etch process, fluorinated etch chemistries in which one ormore commonly utilized gases such as CF₄, CHF₃, C₂F₈, SF₆, among others,are used. In embodiments, aluminum or an alloy of aluminum is used toform the hard mask. Aluminum hard masks are known to exhibit a highresistance to dry etching in fluorinated chemistries and thus thedimensions of the hard mask can be maintained during the etching of theplanar waveguide layer 2405, in which the fiducial marks 2414, thereference pillars, 2434, the planar waveguides 2444 are formed in Step2392 of process flow 2310. In other embodiments, other hard masks areused that also exhibit high resistance to the etch chemistry such as Au,Ag, Ni, and Pt. In other embodiments, hard masks layers such as Ti,TiO_(x), Ta, TaO_(x), aluminum oxide, silicon nitride, silicon carbide,or a combination of one or more of these materials are used. In someembodiments, oxygen or other oxygen-containing gas is added to theetching chemistry to increase the resistance of the hard mask to theetch chemistry. In yet other embodiments, diluents are added to thefluorinated gas chemistry such as one or more of argon, helium,nitrogen, and oxygen, among others to increase the resistance of thehard mask to the fluorinated etch chemistry. In embodiments, the maskinglayer typically has a slow rate of removal in comparison to the rate ofremoval of the planar waveguide layer. Methods for etching of silicondioxide, silicon nitride, and silicon oxynitride are well understood bythose skilled in the art of semiconductor processing, as are methods ofincreasing the resistance of aluminum hard mask layers and other hardmask layers using fluorinated etch chemistries.

After the patterning 2392 of the hard mask layer and planar waveguidelayer to form the fiducial marks 2414, the reference pillars 2434, theplanar waveguides 2444, a mask material is formed over portions of thePIC that includes the hard mask patterned features 2416 a-2416 c. Thismask layer is some embodiments, is a photoresist layer. In otherembodiments, this mask layer is a hard mask layer. In embodiments, themask layer is patterned to expose the underlying patterned hard masklayer portion 2416 b over the patterned waveguides 2444 and to protectthe patterned hard mask layer portion 2416 c over the fiducial marks2414 and the patterned hard mask layer portion 2416 a over the referencepillars 2434. Exposure of the hard mask layer portion 2416 b over thewaveguides, however, enables removal 2393 in process flow 2310 of thehard mask portion 2416 b from the patterned waveguides 2444 without theremoval of the hard mask portions 2416 a and 2416 c from the fiducialmarks 2414 and the z-pillars 2434.

A schematic illustration of features of the PIC after removal of thehard mask portion 2416 b and subsequent removal of the mask layer thatis used in embodiments to protect the hard mask portions 2416 a, 2416 cis shown in FIG. 24D. Removal of the hard mask portion 2416 b (see FIG.24C) from the planar waveguides 2444 of the hard mask layer 2416 isachieved in some embodiments using a wet etch process that selectivelyremoves the metal or other hard mask with little or no removal of theunderlaying planar waveguide layer. Metal etchants, such as those usedfor the removal of an aluminum hard mask, for example, and that havelittle or no effect on waveguide fabricated from silicon nitride andsilicon dioxide, for example, are well known in the art of semiconductorprocessing. In other embodiments, a dry etch process is used. A benefitof a wet etch process to remove the hard mask portion 2416 b from theplanar waveguide 2444 below includes a high preferential selectivity foretching of the hard mask 2416 b with minimal removal of the underlyingplanar waveguides 2444.

Upon completion of the removal step 2393 of the hard mask portion 2416 bfrom the planar waveguides 2444, and removal of the photoresist masklayer that was used to protect the hard mask portions 2416 a and 2416 c,a forming step 2394 is shown in the process flow 2310 to form a thickinsulating dielectric layer 2438 as illustrated in FIG. 24E. The thickdielectric layer 2438 may be one or more layers of silicon dioxide,silicon nitride, or silicon oxynitride, for example, and may include oneor more of a planar waveguide cladding layer, a buffer layer, a spacerlayer, and a passivation layer, among others. In some embodiments, layer2438 includes a planarization layer, and a planarization step is used toplanarize the thick dielectric layer 2438 after this layer is formed.

Step 2395 of the process flow 2310 is a forming step that includes theformation of cavities 2448, 2449, 2469 in the thick dielectric layer2438. This cavity forming step 2395 includes a patterned hard maskforming step as illustrated in FIG. 24F and an etching step asillustrated in FIG. 24G, among others. The hard mask 2417 shown in FIG.24F, is preferably one such as aluminum or from an alloy of aluminum,among others, formed over the insulating layer 2438 and patterned usinga plasma etch process or a wet chemical etch process to expose theportions of the underlying insulating layer 2438 within which cavities2448,2449 is formed, and to expose the portions of the underlyinginsulating layer 2438 within which cavity 2469 is formed. Aluminum andalloys of aluminum, provide a high resistance to fluorinated etchantsused to etch insulating layers such as silicon dioxide, silicon nitride,and silicon oxynitride preferably used in layer 2438. An embodiment ofthe effect of the etching step on the formation of the cavities2448,2449,2469 is illustrated in FIG. 24G. The z-pillars 2434 are shownthat result from the exposure of the buried hard mask portion 2416 athat was formed from the hard mask 2416 in cavity 2448. Exposedfiducials 2414 are also shown that result from the exposure of theburied hard mask portion 2416 c that was formed from the hard mask 2416in cavity 2449. Cavity 2469 is shown having been formed at the edge ofthe PIC 2402. In practice, the cavity 2469 is formed prior tosingulation of the substrate into individual die, and thus the cavity isnot cleaved as shown.

In some embodiments, it is or may not be preferable or necessary toexpose the buried fiducial marks 2414 to obtain the improved clarity ofthe fiducials in subsequent steps in which the fiducials 2414 are usedin the fabrication of the PIC 2402, or for the placement of optical dieonto the PIC 2402. In these embodiments, the patterning step for thehard mask 2417 that is used to expose the areas of the insulating layer2438 to form the cavities 2448 will not include an allowance forexposure of the areas of the insulating layer 2438 to also form cavities2449 to expose the fiducials 2414 within these cavities 2449 asillustrated in FIG. 24G. Improved visibility of the fiducials 2414 is tobe expected upon the formation of the cavity 2449, but may not berequired in some embodiments. Improved visibility of the fiducials maynot be required, for example, in embodiments with thin insulating layers2438, in applications in which the surface of the thick insulating layer2438 remains visibly transparent, and in embodiments in which thecontrast between the fiducials and the underlying layers is adequate.Exposure of the fiducials 2414 with the formation of cavity 2449, ingeneral, provides improved visibility in embodiments for which thecavities 2449 are provided since the focal plane of the fiducial 2414 isshared with the focal plane of the z-pillars 2434 and other alignmentaids formed using the hard mask 2416 in these embodiments. The improvedvisibility also results from the elimination of deleterious effects thatprocessing steps such as mechanical planarization may have on increasingthe opacity of the layer 2438 that might limit the visibility of aburied fiducial. In the embodiment illustrated in FIG. 24G, thealignment pillars 2434 are shown in cavity 2448 and the fiducials 2414are shown in cavity 2449. In other embodiments, the fiducials 2414 areformed in the same cavity 2448 as the alignment reference pillars 2434.In other embodiments, two or more fiducial marks 2414 are formed. Inembodiments with two or more fiducial marks 2414, one or more fiducialmarks 2414 may be formed within the cavity 2448 and one or more fiducialmarks 2414 may be formed in a separate cavity 2449. In yet otherembodiments with two or more fiducial marks 2414, multiple cavities 2449are formed with fiducial marks 2414. The fiducial marks 2414 illustratedherein are shown in the shape of a “+” sign. Other shapes are also usedin embodiments. Effective shapes for fiducial marks are well understoodby those skilled in the art.

In the schematic drawing in FIG. 24H, the PIC 2402 is shown inembodiments after removal of the hard mask 2417 used in the formation ofthe cavities 2448,2449 in the insulating layer 2438.

Fiber optic cables for the delivery and extraction of optical signalsfrom the PICs are typically formed in v-grooves at the edges of the PICsubstrates. In optional forming step 2396, one or more v-grooves 2450are formed in the PIC to accommodate the fiber optic cable attachment.It should be noted that the v-grooves 2450 are typically formed prior tothe completion of the PIC fabrication process, and that the fiber opticcables 2454 are typically not mounted to the PIC 2402 until after thecompletion of the PIC fabrication process and including the completionof the singulation of the substrate into individual PIC die. Thepositioning of the fiber optic cable 2454 into the v-groove 2450,however, is shown in FIG. 24I to illustrate the alignment of the core2456 of the fiber optic cable 2454 with the core of the planar waveguide2444.

In the embodiments shown in FIG. 24 , the alignment and attachment offiber optic cables 2454 in embodiments is further facilitated with theuse of fiber optic cable mounting blocks 2462. Fiber optic cablemounting blocks 2462 enable accurate alignment of the core 2456 of theoptical fiber cables 2454 with a facet 2452 of a planar waveguide 2444on the PIC 2402. FIG. 24I shows an embodiment of a PIC 2402 with a fiberoptic cable 2454 positioned in a v-groove 2450 without the fiber opticmounting block 2462 in place and FIG. 24J shows the embodiment of PIC2402 with the fiber optic cable 2454 positioned in a fiber optic cablemounting block 2462. The fiber optic cable mounting block 2462facilitates the alignment and attachment of the fiber optic cable 2454to the interposer, and in embodiments is held in place in someembodiments with an adhesive or an epoxy.

It should also be noted that although fiber optic cables are used tofacilitate the transfer of optical signals to and from PICs, the use ofthe alignment techniques described herein is not limited by the presenceor lack of a fiber attachment method in embodiments, such as a v-grooveor a method for attachment of a fiber optic cable mounting block.

Significant advantages to the alignment of the core of the fiber opticcable 2454 with the facet 2452 of the planar waveguides 2444 formed inthe planar waveguide layer 2405 are enabled with embodiments describedherein. In the embodiment shown in FIG. 24I, a patterned PR mask isused, for example, to expose the portion of the substrate for theformation of one or more v-grooves. In embodiment in which a photoresistmask is used to expose the locations for the v-grooves, this patternedphotoresist mask protects a least a portion of the PIC during theformation of the v-grooves 2450. The etch process for forming v-groovesis well understood in the art of semiconductor fabrication and istypically formed using a wet etch process.

Referring to FIG. 24J, an embodiment of the PIC 2402 is shown afterformation of the v-groove 2450 and with a fiber optic mounting block2462 in place at the edge of the PIC substrate (after cleaving).Surfaces within the v-groove 2450 form a contact with the cladding layer2455 of a mounted fiber optic cable 2454. FIG. 24J shows the PIC 2402with a portion of a fiber optic cable 2454 positioned in the v-groove2450 and in the fiber optic cable mounting block 2462 to illustrate theuse of these alignment features to align the core 2456 of the fiberoptic cable 2454 with the end facet 2452 (shown in FIG. 24G) of theportion of the planar waveguide 2444 to which the core 2456 is aligned.Alignment of the fiber core 2456 with the waveguide facet 2452 of theplanar waveguide 2444 is beneficial for efficient transfer of opticalsignals between these devices.

The sequence of drawings in FIGS. 24A-24H illustrate the formation ofelements of a self-aligned optoelectrical device structure in aninterposer-based PIC 2402 and include the z-pillars 2434 in cavities2448, the buried planar waveguide structures 2444 that terminate at thewalls of the cavity 2448, and the buried fiducial marks 2414. Thesequence of drawings in FIGS. 24A-24H also illustrate the formation ofan embodiment of a form of v-groove and cavity for the mounting of afiber optic cable mounting block 2462 used to facilitate the mounting ofthe fiber optic cable 2454 and the alignment of the core 2456 of thefiber optic cable 2454 with the end facet 2452 of a portion of a planarwaveguide 2444. Upon formation of the elements of the PIC structure 2402as shown, the alignment features in example embodiments in which opticaldie are positioned into the PIC 2402, as described herein and in FIGS.7M-7P, can be implemented. Additional embodiments of the use of thealignment aids in the attachment and alignment of fiber optic cables areprovides herein.

Referring to FIGS. 25 and 26 , a process flow diagram and a sequence ofdrawings, respectively, are shown that illustrate the steps in theprocess flow for an embodiment that utilizes additional embodiments forusing a fiber optic cable mounting block to mount a fiber optic cable tothe PIC that further includes the use of z-pillars to support the fiberoptic cable mounting block, in addition to the z-pillars used in thesupport and alignment of mounted optical devices elsewhere in the PIC.

Referring to FIG. 25 , a process flowchart is shown for the formation ofinterposer-based PICs with embodiments of the interposer alignmentstructures, and aspects of embodiments described in this flowchart areillustrated in FIG. 26 . In step 2590 of process flow 2510, a planarwaveguide layer 2605 is formed on a base structure, wherein the basestructure 2601 includes an optional electrical interconnect layer 2603on a substrate 2600. The planar waveguide layer 2605 on base structure2601 forms interposer 2604. The electrical interconnect layer 2603, asshown in FIG. 26A is formed in some embodiments on a semiconductorsubstrate 2600 such as silicon, indium phosphide, gallium arsenide, orsome other semiconductor. In other embodiments, a ceramic or insulatingsubstrate is used. In yet other embodiments, a metal substrate is used.And in yet other embodiments, a combination of one or more semiconductorlayers, insulating layers, and metal layers are used to form a substrate2600 upon which the optional electrical interconnect layer 2603 and theplanar waveguide layer 2605 are formed. In some embodiments, theelectrical interconnect layer 2603 is not in direct contact with thesubstrate but rather an intervening layer is present. Similarly, theplanar waveguide layer 2605, in some embodiments, is not in directcontact with the underlying electrical interconnect layer 2603 butrather an intervening layer or layers may be present. In someembodiments, a semiconductor layer or substrate is mounted on a metallayer or substrate to form a composite substrate.

In hard mask layer formation step 2591 of the process flow 2510, apatterned hard mask 2616 is formed on the planar waveguide layer 2605.Hard mask layer 2616 includes patterning for the formation of theoptical waveguides and all or a portion of the alignment aids that areformed from the planar waveguide layer 2605. In the embodiments in FIG.26B, the hard mask layer includes patterns for alignment aids thatinclude fiducial marks and alignment pillars or z-pillars. In theembodiments shown in FIGS. 26B, hard mask layer portions 2616 a and 2616d show hard mask patterns for an embodiment of a z-pillar alignment aidswhich are shown after the hard mask patterning step in FIG. 26B;Similarly, hard mask portion 2616 b shows a hard mask pattern for anembodiment of a planar waveguide 2644 which is shown after patterning inFIG. 26B. Hard mask portion 2616 c shows a hard mask pattern for anembodiment of a fiducial mark alignment aid which is shown after hardmask patterning in FIG. 26B. In summary, in the embodiment shown in FIG.26B, portions of the patterned hard mask include the z-pillar portions2616 a, 2616 d, planar waveguide portion 2616 b, and fiducial markportion 2616 c. These portions of the hard mask 2616 are used to patternthe z-pillars used to support and align mounted optical devices andfurther to facilitate the alignment and attachment of fiber optic cablemounting blocks, and to pattern the planar waveguides 2644 and thefiducial marks 2614 using an etch process to remove the planar waveguidelayer 2605 from areas not protected by the hard mask layer 2616 as shownin FIG. 26C.

Portions of the hard mask layer 2616, are also used in some embodimentsto form all or a portion of optical devices 2640 for embodiments inwhich the optical devices 2640 are formed wholly or in part from theplanar waveguide layer 2605. Optical devices 2640 may be waveguides,gratings, lens, or any device that can be formed from at least a portionof the planar waveguide layer. Alternatively, in other embodiments,optical devices 2640 are mounted devices, and not fabricated directlyfrom the planar waveguide layer 2605 but added at a later step in theprocess of forming the PIC 2602. Optical device 2640 can be one or moreof a portion of a device formed from the planar waveguide layer and oneor more of a portion of a mounted device.

In some embodiments, the planar waveguide layer 2605 is formed of one ormore layers of silicon dioxide, silicon nitride, and silicon oxynitrideas described herein. To pattern the planar waveguides from such layersusing a dry etch process, fluorinated etch chemistries in which one ormore commonly utilized gases such as CF₄, CHF₃, C₂F₈, SF₆, among others,are used. In embodiments, aluminum or an alloy of aluminum is used toform the hard mask. Aluminum hard masks are known to exhibit a highresistance to dry etching in fluorinated chemistries and thus thedimensions of the hard mask can be maintained during the etching of theplanar waveguide layer 2605, in which the fiducial marks 2614, thereference pillars, 2634, the planar waveguides 2644 are formed in Step2592 of process flow 2510. In other embodiments, other hard masks areused that also exhibit high resistance to the etch chemistry such as Au,Ag, Ni, and Pt. In other embodiments, hard masks layers such as Ti,TiO_(x), Ta, TaO_(x), aluminum oxide, silicon nitride, silicon carbide,or a combination of one or more of these materials are used. In someembodiments, oxygen or other oxygen-containing gas is added to theetching chemistry to increase the resistance of the hard mask to theetch chemistry. In yet other embodiments, diluents are added to thefluorinated gas chemistry such as one or more of argon, helium,nitrogen, and oxygen, among others to increase the resistance of thehard mask to the fluorinated etch chemistry. In embodiments, the maskinglayer typically has a slow rate of removal in comparison to the rate ofremoval of the planar waveguide layer. Methods for etching of silicondioxide, silicon nitride, and silicon oxynitride are well understood bythose skilled in the art of semiconductor processing, as are methods ofincreasing the resistance of aluminum hard mask layers and other hardmask layers using fluorinated etch chemistries.

After the patterning 2592 of the planar waveguide layer to form thefiducial marks 2614, the reference pillars 2634, the planar waveguides2644, a mask material is formed over portions of the PIC that includesthe hard mask patterned features 2616 a-2616 d. This mask layer is someembodiments, is a photoresist layer. In other embodiments, this masklayer is a hard mask layer. In embodiments, the mask layer is patternedto expose the underlying patterned hard mask layer portion 2616 b overthe patterned waveguides 2644 and to protect the patterned hard masklayer portion 2616 c over the fiducial marks 2614 and the patterned hardmask layer portion 2616 a 2616 d over the reference pillars 2634.Exposure of the hard mask layer portion 2616 b over the waveguides,however, enables removal 2593 in process flow 2510 of the hard maskportion 2616 b from the patterned waveguides 2644 without the removal ofthe hard mask portions 2616 a and 2616 c from the fiducial marks 2614and the z-pillars 2634.

A schematic illustration of features of the PIC after removal of thehard mask portion 2616 b and subsequent removal of the mask layer thatis used in embodiments to protect the hard mask portions 2616 a, 2616 c,2616 d is shown in FIG. 26D. Removal of the hard mask portion 2616 b(see FIG. 26C) from the planar waveguides 2644 of the hard mask layer2616 is achieved in some embodiments using a wet etch process thatselectively removes the metal or other hard mask with little or noremoval of the underlaying planar waveguide layer. Metal etchants, suchas those used for the removal of an aluminum hard mask, for example, andthat have little or no effect on waveguide fabricated from siliconnitride and silicon dioxide, for example, are well known in the art ofsemiconductor processing. In other embodiments, a dry etch process isused. A benefit of a wet etch process to remove the hard mask portion2616 b from the planar waveguide 2644 below includes a high preferentialselectivity for etching of the hard mask 2616 b with minimal removal ofthe underlying planar waveguides 2644.

Upon completion of the removal step 2593 of the hard mask portion 2616 bfrom the planar waveguides 2644, and removal of the photoresist masklayer that was used to protect the hard mask portions 2616 a, 2616 c,and 2616 d, a forming step 2594 is shown in the process flow 2510 toform a thick insulating dielectric layer 2638 as illustrated in FIG.26E. The thick dielectric layer 2638 may be one or more layers ofsilicon dioxide, silicon nitride, or silicon oxynitride, for example,and may include one or more of a planar waveguide cladding layer, abuffer layer, a spacer layer, and a passivation layer, among others. Insome embodiments, layer 2638 includes a planarization layer, and aplanarization step is used to planarize the thick dielectric layer 2638after this layer is formed.

Step 2595 of the process flow 2510 is a forming step that includes theformation of cavities 2648, 2649, 2669 in the thick dielectric layer2638. This cavity forming step 2595 includes a patterned hard maskforming step as illustrated in FIG. 26F and an etching step asillustrated in FIG. 26G, among others. The hard mask 2617 shown in FIG.26F, is preferably one such as aluminum or from an alloy of aluminum,among others, formed over the insulating layer 2638 and patterned usinga plasma etch process or a wet chemical etch process to expose theportions of the underlying insulating layer 2638 within which cavities2648,2649 is formed, and to expose the portions of the underlyinginsulating layer 2638 within which cavity 2669 is formed. Aluminum andalloys of aluminum, provide a high resistance to fluorinated etchantsused to etch insulating layers such as silicon dioxide, silicon nitride,and silicon oxynitride preferably used in layer 2638. An embodiment ofthe effect of the etching step on the formation of the cavities2648,2649,2669 is illustrated in FIG. 26G. The z-pillars 2634 are shownthat result from the exposure of the buried hard mask portion 2616 athat was formed from the hard mask 2616 in cavity 2648 and hard maskportion 2616 d that was formed from the hard mask 2616 in cavity 2669.Exposed fiducials 2614 are also shown that result from the exposure ofthe buried hard mask portion 2616 c that was formed from the hard mask2616 in cavity 2649. Cavity 2669 is shown having been formed at the edgeof the PIC 2602. In practice, the cavity 2669 is formed prior tosingulation of the substrate into individual die, and thus the cavity isnot yet cleaved as shown.

In some embodiments, it is or may not be preferable or necessary toexpose the buried fiducial marks 2614 to obtain the improved clarity ofthe fiducials in subsequent steps in which the fiducials 2614 are usedin the fabrication of the PIC 2602, or for the placement of optical dieonto the PIC 2602. In these embodiments, the patterning step for thehard mask 2617 that is used to expose the areas of the insulating layer2638 to form the cavities 2648 will not include an allowance forexposure of the areas of the insulating layer 2638 to also form cavities2649 to expose the fiducials 2614 within these cavities 2649 asillustrated in FIG. 26G. Improved visibility of the fiducials 2614 is tobe expected upon the formation of the cavity 2649, but may not berequired in some embodiments. Improved visibility of the fiducials maynot be required, for example, in embodiments with thin insulating layers2638, in applications in which the surface of the thick insulating layer2638 remains visibly transparent, and in embodiments in which thecontrast between the fiducials and the underlying layers is adequate.Exposure of the fiducials 2614 with the formation of cavity 2649, ingeneral, provides improved visibility in embodiments for which thecavities 2649 are provided since the focal plane of the fiducial 2614 isshared with the focal plane of the z-pillars 2634 and other alignmentaids formed using the hard mask 2616 in these embodiments. The improvedvisibility also results from the elimination of deleterious effects thatprocessing steps such as mechanical planarization may have on increasingthe opacity of the layer 2638 that might limit the visibility of aburied fiducial. In the example embodiment illustrated in FIG. 26G, thealignment pillars 2634 are shown in cavity 2648 and the fiducials 2614are shown in cavity 2649. In other embodiments, the fiducials 2614 areformed in the same cavity 2648 as the alignment reference pillars 2634.In other embodiments, two or more fiducial marks 2614 are formed. Inembodiments with two or more fiducial marks 2614, one or more fiducialmarks 2614 may be formed within the cavity 2648 and one or more fiducialmarks 2614 may be formed in a separate cavity 2649. In yet otherembodiments with two or more fiducial marks 2614, multiple cavities 2649are formed with fiducial marks 2614. The fiducial marks 2614 illustratedherein are shown in the shape of a “+” sign. Other shapes are also usedin embodiments. Effective shapes for fiducial marks are well understoodby those skilled in the art.

In the schematic drawing in FIG. 26H, the PIC 2602 is shown inembodiments after removal of the hard mask 2617 used in the formation ofthe cavities 2648,2649 in the insulating layer 2638.

Fiber optic cables for the delivery and extraction of optical signalsfrom the PICs are typically formed in v-grooves at the edges of the PICsubstrates. In optional forming step 2596, one or more v-grooves 2650are formed in the PIC to accommodate the fiber optic cable attachment.It should be noted that the v-grooves 2650 are typically formed prior tothe completion of the PIC fabrication process, and that the fiber opticcables 2654 are typically not mounted to the PIC 2602 until after thecompletion of the PIC fabrication process and including the completionof the singulation of the substrate into individual PIC die. PIC die aretypically processed at the wafer level, common in semiconductorfabrication, and then diced into individual discrete PIC devices 2602.The positioning of the fiber optic cable 2654 into the v-groove 2650,however, is shown in FIG. 26I to illustrate the alignment of the core2656 of the fiber optic cable 2654 with the core of the planar waveguide2644.

In the embodiments shown in FIG. 26 , the alignment and attachment offiber optic cables 2654 in embodiments is further facilitated with theuse of fiber optic cable mounting blocks 2662. Fiber optic cablemounting blocks 2662 enable accurate alignment of the core 2656 of theoptical fiber cables 2654 with a facet 2652 of a planar waveguide 2644on the PIC 2602. FIG. 26I shows an embodiment of a PIC 2602 with a fiberoptic cable 2654 positioned in a v-groove 2650 without the fiber opticmounting block 2662 in place and FIG. 26J shows the embodiment of PIC2602 with the fiber optic cable 2654 positioned in a fiber optic cablemounting block 2662. The fiber optic cable mounting block 2662facilitates the alignment and attachment of the fiber optic cable 2654to the interposer, and in embodiments is held in place in someembodiments with an adhesive or an epoxy.

It should also be noted that although fiber optic cables are used tofacilitate the transfer of optical signals to and from PICs, the use ofthe alignment techniques described herein is not limited by the presenceor lack of a fiber attachment method in embodiments, such as a v-grooveor a fiber optic cable mounting block.

Significant advantages to the alignment of the core of the fiber opticcable 2654 with the facet 2652 of the planar waveguides 2644 formed inthe planar waveguide layer 2605 are enabled with embodiments describedherein. In the embodiment shown in FIG. 26I, a patterned PR mask isused, for example, to expose the portion of the substrate for theformation of one or more v-grooves. In embodiment in which a photoresistmask is used to expose the locations for the v-grooves, this patternedphotoresist mask protects a least a portion of the PIC during theformation of the v-grooves 2650. The etch process for forming v-groovesis well understood in the art of semiconductor fabrication and istypically formed using a wet etch process.

Referring to FIG. 26J, an embodiment of the PIC 2602 is shown afterformation of the v-groove 2650 and with a fiber optic mounting block2662 in place at the edge of the PIC substrate (after cleaving).Surfaces within the v-groove 2650 form a contact with the cladding layer2655 of a mounted fiber optic cable 2654. FIG. 26J shows the PIC 2602with a portion of a fiber optic cable 2654 positioned in the v-groove2650 and in the fiber optic cable mounting block 2662 to illustrate theuse of these alignment features to align the core 2656 of the fiberoptic cable 2654 with the end facet 2652 (shown for example, in FIG.26G) of the portion of the planar waveguide 2644 to which the core 2656is aligned. Alignment of the fiber core 2656 with the waveguide facet2652 of the planar waveguide 2644 is beneficial for efficient transferof optical signals between these devices. Alignment of the fiber opticcable 2654 with a facet 2652 of a planar waveguide 2644 on the PIC isfacilitated with the presence of the z-pillars in the cavity 2669.Referring to FIG. 26K, end views of embodiments are shown in which thez-pillars are used as an alignment aid for aligning a fiber optic cablemounting block 2662. The top surface of the z-pillar alignment aids inFIG. 26K(i) are shown in contact with the base 2664 of the fiber opticcable mounting block 2662. In embodiments, the heights of the z-pillars2634 and the dimensions of the fiber optic cable mounting blockcomponents including the base 2664, the lid 2666, and including thedimensions of the v-grooves in the base 2664 and the lid 2666 are suchthat alignment between the fiber optic cable core 2655 and the end facet(e.g, facet 2652) of a planar waveguide 2644 is achieved to facilitatethe transfer of optical signals between the core 2655 and a waveguide2644. Referring to FIG. 26K(ii), another embodiment is shown in whichthe fiber optic cable mounting block has notched feature 2671 to providea lateral constraint alignment feature to constrain movement in thex-direction as shown (see reference coordinate system in FIG. 26K(ii).)Notch 2671 and z-pillar 2634 in FIG. 26K(ii) further facilitate thealignment between the core 2655 of the fiber optic cable 2654 and thefacet of a planar waveguide 2644 on PIC 2602. In other embodiments, thenotch 2671 in the fiber optic cable mounting block 2662 is formed toaccommodate lateral constraint in both the x- and y-directions, as forexample, feature 581 in FIG. 5C.

The sequence of drawings in FIGS. 26A-26K illustrate the formation ofelements of a self-aligned optoelectrical device structure in aninterposer-based PIC 2602 and include the z-pillars 2634 in cavities2648, 2649, 2669, the buried planar waveguide structures 2644 thatterminate at the walls of the cavity 2648, and the buried fiducial marks2614. The sequence of drawings in FIGS. 26A-26K illustrate the formationof an embodiment of z-pillars in conjunction with a v-groove and cavityfor the mounting of a fiber optic cable mounting block 2662 used tofacilitate the mounting of the fiber optic cable 2654 and to facilitatethe alignment of the core 2656 of the fiber optic cable 2654 with theend facet 2652 of a portion of a planar waveguide 2644. Upon formationof the elements of the PIC structure 2602 as shown, the alignmentfeatures in example embodiments in which optical die are positioned intothe PIC 2602, as described herein and in FIGS. 7M-7P, can beimplemented. Additional embodiments of the use of the alignment aids inthe attachment and alignment of fiber optic cables are provides herein.

Referring to FIGS. 27 and 28 , a process flow diagram and a sequence ofdrawings, respectively, are shown that illustrate the steps in theprocess flow for an embodiment that utilizes a fiber optic cablemounting block with the use of a lateral constraint alignment featurederived from the planar waveguide layer. In this embodiment, asdescribed in FIG. 27 and FIGS. 28 , z-pillar alignment aids are notincluded for the fiber optic cable mounting block.

Referring to FIG. 27 , a process flowchart is shown for the formation ofinterposer-based PICs with embodiments of the interposer alignmentstructures, and aspects of embodiments described in this flowchart areillustrated in FIG. 28 . In step 2790 of process flow 2710, a planarwaveguide layer 2805 is formed on a base structure, wherein the basestructure 2801 includes an optional electrical interconnect layer 2803on a substrate 2800. The planar waveguide layer 2805 on base structure2801 forms interposer 2804. The electrical interconnect layer 2803, asshown in FIG. 28A is formed in some embodiments on a semiconductorsubstrate 2800 such as silicon, indium phosphide, gallium arsenide, orsome other semiconductor. In other embodiments, a ceramic or insulatingsubstrate is used. In yet other embodiments, a metal substrate is used.And in yet other embodiments, a combination of one or more semiconductorlayers, insulating layers, and metal layers are used to form a substrate2800 upon which the optional electrical interconnect layer 2803 and theplanar waveguide layer 2805 are formed. In some embodiments, theelectrical interconnect layer 2803 is not in direct contact with thesubstrate but rather an intervening layer is present. Similarly, theplanar waveguide layer 2805, in some embodiments, is not in directcontact with the underlying electrical interconnect layer 2803 butrather an intervening layer or layers may be present. In someembodiments, a semiconductor layer or substrate is mounted on a metallayer or substrate to form a composite substrate.

In hard mask layer formation step 2791 of the process flow 2710, a hardmask 2816 is formed on the planar waveguide layer 2805. Hard mask layer2816 includes patterning for the formation of the optical waveguides andall or a portion of the alignment aids that are formed from the planarwaveguide layer 2805. In the embodiments in FIG. 28B, the hard masklayer includes patterns for alignment aids that include fiducial marks,the alignment pillars or z-pillars, and v-groove alignment aids. In theembodiments shown in FIGS. 28B, hard mask layer portion 2816 a shows ahard mask pattern for an embodiment of a z-pillar alignment aid which isshown after the hard mask patterning step in FIG. 28B; Similarly, hardmask portion 2816 b shows a hard mask pattern for an embodiment of aplanar waveguide 2844 which is shown after patterning in FIG. 28B. Hardmask portion 2816 c shows a hard mask pattern for an embodiment of afiducial mark alignment aid which is shown after hard mask patterning inFIG. 28B. And hard mask portion 2816 d shows a hard mask pattern for anembodiment of a v-groove alignment aid 2851 which is shown after hardmask patterning in FIG. 28B. In the embodiment in FIG. 28 , the v-groovealignment aid feature 2851 is used to position a v-groove for placementof a fiber optic cable as further described herein. In some embodiments,as described herein, the v-groove alignment aid 2851 functions as alateral constraint. For the hard mask in the embodiment shown in FIG.28B, portions of the patterned hard mask include the z-pillar portion2816 a, planar waveguide portion 2816 b, fiducial mark portion 2816 c,and v-groove alignment aid portion 2816 d. These portions of the hardmask 2816 are used to pattern the z-pillars 2834, the planar waveguides2844, the fiducial marks 2814, and the v-groove alignment aid 2851,respectively, using an etch process to remove the planar waveguide layer2805 from areas not protected by the hard mask layer 2816 as shown inFIG. 28C.

Portions of the hard mask layer 2816, are also used in some embodimentsto form all or a portion of optical devices 2840 for embodiments inwhich the optical devices 2840 are formed wholly or in part from theplanar waveguide layer 2805. Optical devices 2840 may be waveguides,gratings, lens, or any device that can be formed from at least a portionof the planar waveguide layer. Alternatively, in other embodiments,optical devices 2840 are mounted devices, and not fabricated directlyfrom the planar waveguide layer 2805 but added at a later step in theprocess of forming the PIC 2802. Optical device 2840 can be one or moreof a portion of a device formed from the planar waveguide layer and oneor more of a portion of a mounted device.

In some embodiments, the planar waveguide layer 2805 is formed of one ormore layers of silicon dioxide, silicon nitride, and silicon oxynitrideas described herein. To pattern the planar waveguides from such layersusing a dry etch process, fluorinated etch chemistries in which one ormore commonly utilized gases such as CF₄, CHF₃, C₂F₈, SF₆, among others,are used. In embodiments, aluminum or an alloy of aluminum is used toform the hard mask. Aluminum hard masks are known to exhibit a highresistance to dry etching in fluorinated chemistries and thus thedimensions of the hard mask can be maintained during the etching of theplanar waveguide layer 2805, in which the fiducial marks 2814, thereference pillars, 2834, the planar waveguides 2844, and the v-groovealignment aid or lateral constraint 2851 are formed in Step 2792 ofprocess flow 2710. In other embodiments, other hard masks are used thatalso exhibit high resistance to the etch chemistry such as Au, Ag, Ni,and Pt. In other embodiments, hard masks layers such as Ti, TiO_(x), Ta,TaO_(x), aluminum oxide, silicon nitride, silicon carbide, or acombination of one or more of these materials are used. In someembodiments, oxygen or other oxygen-containing gas is added to theetching chemistry to increase the resistance of the hard mask to theetch chemistry. In embodiments, the masking layer typically has a slowrate of removal in comparison to the rate of removal of the planarwaveguide layer. In yet other embodiments, diluents are added to thefluorinated gas chemistry such as one or more of argon, helium,nitrogen, and oxygen, among others to increase the resistance of thehard mask to the fluorinated etch chemistry. Methods for etching ofsilicon dioxide, silicon nitride, and silicon oxynitride are wellunderstood by those skilled in the art of semiconductor processing, asare methods of increasing the resistance of aluminum hard mask layersand other hard mask layers using fluorinated etch chemistries. Otherwaveguide materials are used in other embodiments.

After the patterning 2792 of the fiducial marks 2814, the referencepillars 2834, the planar waveguides 2844, and the v-groove alignmentaids 2851, a mask material is formed over portions of the PIC thatincludes the hard mask patterned features 2816 a-2816 d. This mask layeris some embodiments, is a photoresist layer. In other embodiments, thismask layer is a hard mask layer. In embodiments, the mask layer ispatterned to expose the underlying patterned hard mask layer portion2816 b over the patterned waveguides 2844 and to protect the patternedhard mask layer portion 2816 a over the reference pillars 2834, thepatterned hard mask layer portion 2816 c over the fiducial marks 2814,and optionally protect the hard mask portion 2816 d over the v-groovealignment aid 2851. Exposure of the hard mask layer portion 2816 b overthe waveguides, however, enables removal 2793 in process flow 2710 ofthe hard mask portion 2816 b from the patterned waveguides 2844 withoutthe removal of the hard mask portions 2816 a and 2816 c from thefiducial marks 2814 and the z-pillars 2834, and optionally from hardmask portion 2816 d from the v-groove alignment aid 2851. In someembodiments, removal of the hard mask portion 2816 d is preferred.

A schematic illustration of features of the PIC after removal of thehard mask portion 2816 b and subsequent removal of the mask layer thatis used in embodiments to protect the hard mask portions 2816 a, 2816 c,2816 d is shown in FIG. 28D. Removal of the hard mask portion 2816 b(see FIG. 28C) from the planar waveguides 2844 of the hard mask layer2816 is achieved in some embodiments using a wet etch process thatselectively removes the metal or other hard mask with little or noremoval of the underlaying planar waveguide layer. Metal etchants, suchas those used for the removal of an aluminum hard mask, for example, andthat have little or no effect on waveguide fabricated from siliconnitride and silicon dioxide, for example, are well known in the art ofsemiconductor processing. In other embodiments, a dry etch process isused. A benefit of a wet etch process, such as a phosphoric acid-basedchemistry, to remove the hard mask portion 2816 b from the planarwaveguide 2844 below includes a high preferential selectivity foretching of the hard mask 2816 b with minimal removal of the underlyingplanar waveguides 2844.

Upon completion of the removal step 2793 of the hard mask portion 2816 bfrom the planar waveguides 2844, and removal of the photoresist masklayer that was used to protect the hard mask portions 2816 a and 2816 c,and optionally 2816 d, a forming step 2794 is shown in the process flow2710 to form a thick insulating dielectric layer 2838 as illustrated inFIG. 28E. The thick dielectric layer 2838 may be one or more layers ofsilicon dioxide, silicon nitride, or silicon oxynitride, for example,and may include one or more of a planar waveguide cladding layer, abuffer layer, a spacer layer, and a passivation layer, among others. Insome embodiments, layer 2838 includes a planarization layer, and aplanarization step is used to planarize the thick dielectric layer 2838after this layer is formed.

Step 2795 of the process flow 2710 is a forming step that includes theformation of cavities 2848, 2849, 2869 in the thick dielectric layer2838. This cavity forming step 2795 includes a patterned hard maskforming step as illustrated in FIG. 28F and an etching step asillustrated in FIG. 28G, among others. The hard mask 2817 shown in FIG.28F, is preferably one such as aluminum or from an alloy of aluminum,among others, formed over the insulating layer 2838 and patterned usinga plasma etch process or a wet chemical etch process to expose theportions of the underlying insulating layer 2838 within which cavities2848,2849 is formed, and to expose the portions of the underlyinginsulating layer 2838 within which cavity 2869 is formed. Aluminum andalloys of aluminum, provide a high resistance to fluorinated etchantsused to etch insulating layers such as silicon dioxide, silicon nitride,and silicon oxynitride preferably used in layer 2838. The effect of theetching step on the formation of the cavities 2848,2849,2869 isillustrated in the embodiment shown in FIG. 28G. The z-pillars 2834 areshown that result from the exposure of the buried hard mask portion 2816a that was formed from the hard mask 2816 in cavity 2848. Exposedfiducials 2814 are also shown that result from the exposure of theburied hard mask portion 2816 c that was formed from the hard mask 2816in cavity 2849. Cavity 2869 is shown having been formed at the edge ofthe PIC 2802. In practice, the cavity 2869 is formed prior tosingulation of the substrate into individual die, and thus the cavity isnot yet cleaved as shown but rather is shown as the singulated devicewill appear after singulation.

In some embodiments, it is or may not be preferable or necessary toexpose the buried fiducial marks 2814 to obtain the improved clarity ofthe fiducials in subsequent steps in which the fiducials 2814 are usedin the fabrication of the PIC 2802, or for the placement of optical dieonto the PIC 2802. In these embodiments, the patterning step for thehard mask 2817 that is used to expose the areas of the insulating layer2838 to form the cavities 2848 will not include an allowance forexposure of the areas of the insulating layer 2838 to also form cavities2849 to expose the fiducials 2814 within these cavities 2849 asillustrated in FIG. 28G. Improved visibility of the fiducials 2814 is tobe expected upon the formation of the cavity 2849, but may not berequired in some embodiments. Improved visibility of the fiducials maynot be required, for example, in embodiments with thin insulating layers2838, in applications in which the surface of the thick insulating layer2838 remains visibly transparent, and in embodiments in which thecontrast between the fiducials and the underlying layers is adequate.Exposure of the fiducials 2814 with the formation of cavity 2849, ingeneral, provides improved visibility in embodiments for which thecavities 2849 are provided since the focal plane of the fiducial 2814 isshared with the focal plane of the z-pillars 2834 and other alignmentaids formed using the hard mask 2816 in these embodiments. The improvedvisibility also results from the elimination of deleterious effects thatprocessing steps such as mechanical planarization may have on increasingthe opacity of the layer 2838 that might limit the visibility of aburied fiducial. In the example embodiment illustrated in FIG. 28G, thealignment pillars 2834 are shown in cavity 2848 and the fiducials 2814are shown in cavity 2849. In other embodiments, the fiducials 2814 areformed in the same cavity 2848 as the alignment reference pillars 2834.In other embodiments, two or more fiducial marks 2814 are formed. Inembodiments with two or more fiducial marks 2814, one or more fiducialmarks 2814 may be formed within the cavity 2848 and one or more fiducialmarks 2814 may be formed in a separate cavity 2849. In yet otherembodiments with two or more fiducial marks 2814, multiple cavities 2849are formed with fiducial marks 2814. The fiducial marks 2814 illustratedherein are shown in the shape of a “+” sign. Other shapes are also usedin embodiments. Effective shapes for fiducial marks are well understoodby those skilled in the art.

Also shown in the embodiments in FIG. 28G and FIG. 28H, is the v-groovealignment aid 2851. This v-groove alignment aid 2851 is exposed in theseembodiments using the same patterned hard mask 2817 and etch processused in the formation of one or more of the cavities 2848, 2849. Anaspect of embodiments is the use of a common lithographic patterningstep to define the v-groove alignment aid 2851 with the planar waveguide2844 to provide lithographic level of alignment between these featuresof a PIC using the techniques described herein. The v-groove is used inembodiments to position a fiber optic cable such that the core isaligned in embodiments with a portion of a planar waveguide 2844. Andalthough the patterning of the v-groove alignment aid 2851 from theplanar waveguide layer, in embodiments, is performed concurrently withthe patterning of the fiducials 2814, the planar waveguides 2844, andthe z-pillars 2834, the subsequent removal of the oxide 2838 to exposethe v-groove alignment feature 2851 from within the oxide 2838 need notbe performed concurrently with the formation of the cavities 2848, 2849.

In the schematic drawing in FIG. 28H, the PIC 2802 is shown inembodiments after removal of the hard mask 2817 used in the formation ofthe cavities 2848,2849 in the insulating layer 2838, and removal of theoxide 2838 in proximity to the alignment aid 2851 as shown, for example,in the FIG. 28H.

Fiber optic cables for the delivery and extraction of optical signalsfrom the PICs are typically formed in v-grooves at the edges of the PICsubstrates. In optional forming step 2796, one or more v-grooves 2850are formed in the PIC to accommodate the fiber optic cable attachment.It should be noted that the v-grooves 2850 are typically formed prior tothe completion of the PIC fabrication process, and that the fiber opticcables 2854 are typically not mounted to the PIC 2802 until after thecompletion of the PIC fabrication process and including the completionof the singulation of the substrate into individual PIC die.

In the embodiments shown in FIG. 28 , the alignment and attachment offiber optic cables 2854 in embodiments is further facilitated with theuse of fiber optic cable mounting blocks 2862. Fiber optic cablemounting blocks 2862 enable accurate alignment of the core 2856 of theoptical fiber cables 2854 with a facet 2852 of a planar waveguide 2844on the PIC 2802. The embodiments shown in FIG. 28 include provisions forthe fiber optic cable mounting block and v-grooves.

Prior to completion of the PIC 2802, the v-grooves that are commonlyformed on the PIC substrates to accommodate the attachment of fiberoptic cables for the delivery and extraction of optical signals from thePIC 2802 are typically formed. FIG. 28I and FIG. 28J show an embodimentin which a v-groove is formed in conjunction with an alignment aid 2851patterned from the planar waveguide layer 2805.

Significant advantages to the alignment of the core of the fiber opticcable 2854 with the facet 2852 of the planar waveguides 2844 formed inthe planar waveguide layer 2805 are enabled with embodiments describedherein. The use of the patterned planar waveguide layer 2805 tosimultaneously form the alignment aid 2851 and to form the waveguides2844, provides lithographic-level resolution for the ultimate alignmentof the fiber optic core 2856 placed within the v-groove alignment aid2851 and the waveguide facet 2852 of the planar waveguides 2844 to whichthe core 2856 of a fiber optic cable 2854 is aligned. In the embodimentshown in FIG. 28I, a patterned PR mask is used, for example, to exposethe portion of the substrate for the formation of one or more v-groovesin proximity with an alignment aid 2851. In embodiment in which aphotoresist mask is used to expose the locations for the v-grooves, thispatterned photoresist mask protects a least a portion of the PIC duringthe formation of the v-grooves 2850. The etch process for formingv-grooves is well understood in the art of semiconductor fabrication andis typically formed using a wet etch process.

Referring to FIG. 28J, an embodiment of the PIC 2802 is shown afterformation of the v-groove 2850 and removal of the photoresist mask 2853used in the formation of the v-groove. Surfaces within the v-groove 2850form a contact with the cladding layer 2855 of a mounted fiber opticcable 2854.

FIG. 28K shows the PIC 2802 with a portion of a fiber optic cable 2854positioned in the v-groove 2850 and in the fiber optic cable mountingblock 2862 to illustrate the use of these alignment features to alignthe core 2856 of the fiber optic cable 2854 with the end facet 2852(shown in FIG. 28G) of the portion of the planar waveguide 2844 to whichthe core 2856 is aligned. Alignment of the fiber core 2856 with thewaveguide facet 2852 of the planar waveguide 2844 is beneficial forefficient transfer of optical signals between these devices. The fiberoptic cable mounting block 2862 facilitates the alignment and attachmentof the fiber optic cable 2854 to the interposer, and in embodiments isheld in place with an adhesive or an epoxy, for example.

It should also be noted that although fiber optic cables are used tofacilitate the transfer of optical signals to and from PICs, the use ofthe alignment techniques described herein is not limited by the presenceor lack of a fiber attachment method in embodiments, such as a v-grooveor a method for attachment of a fiber optic cable mounting block.

The sequence of drawings in FIGS. 28A-28K illustrate the formation ofelements of a self-aligned optoelectrical device structure in aninterposer-based PIC 2802 and include the z-pillars 2834 in cavities2848, the buried planar waveguide structures 2844 that terminate at thewalls of the cavity 2848, the fiducial marks 2814, and the fiber opticcable block alignment aids 2851. The sequence of drawings in FIGS.28A-28K also illustrate the formation of an embodiment of a v-groove forthe alignment and mounting of a fiber optic cable in conjunction withthe mounting block 2862. The mounting block 2862 is used in embodimentsto facilitate the mounting of the fiber optic cable 2854 and thealignment of the core 2856 of the fiber optic cable 2854 with the endfacet 2852 of a portion of a planar waveguide 2844. Upon formation ofthe elements of the PIC structure 2802 as shown, the alignment featuresin example embodiments in which optical die are positioned into the PIC2802, as described herein and in FIGS. 7M-7P, can be implemented.Additional embodiments of the use of the alignment aids in theattachment and alignment of fiber optic cables are provides herein.

In FIGS. 23-28 , a number of process flows and process flow sequencesare described for embodiments that utilize fiber optic cable mountingblocks and other alignment aids that include: (1) an embodiment thatdoes not use z-pillars or a lateral constraint derived from the planarwaveguide layer as shown in in FIGS. 23 and 24 , (2) an embodiment thatdoes include z-pillars to support alignment of the fiber optic cablemounting block but that does not include a lateral constraint alignmentfeature derived from the planar waveguide layer as shown in FIGS. 25 and26 , and (3) an embodiment that does not include the z-pillars but doesinclude the lateral constraint alignment feature derived from the planarwaveguide layer as shown in FIGS. 27 and 28 . The example embodimentsshown in FIGS. 23-28 illustrate various configurations of alignment aidsused in support of the fiber optic cable mounting blocks on interposersubstrates. Further variations in the utilization and implementation ofthe various alignment aids described herein should be evident to thoseskilled in the art.

One such embodiment that includes both the z-pillars 2934 b and analignment aid 2951 formed from the planar waveguide layer 2905 thatcontributes to the alignment of the fiber optic cable mounting block2962 and, more specifically, to the alignment of the fiber optic core2956 of a fiber cable 2954 mounted within the fiber optic mounting block2962 to a facet 2952 of a planar waveguide 2944 on an interposer-basedPIC is shown in FIG. 29A and FIG. 29B. In FIG. 29B, the fiber opticcable mounting block is shown and includes the base 2964 and the lid2966 within which the fiber cable is mounted.

FIG. 29A also shows PIC 2902 with z-pillar alignment aids 2934 a incavity 2948 and fiducial 2914 in cavity 2949. Planar waveguides 2944intersect with the walls of cavity 2948 for so that the optical featuresof optical die mounted within the cavities 2948 can be aligned with theoptical facets of the portions of the planar waveguides 2944 thatintersect with the cavities 2948. In the embodiment shown in FIG. 29Aand FIG. 29B, the z-pillars 2948 b are formed using the same hard masklayer as the hard mask used to form the z-pillars 2948 a. In otherembodiments, different hard mask patterning steps are used to form thez-pillars 2934 a and the z-pillars 2948 b. Significant improvements inthe degree of precision within with the various features of the PIC 2902can be aligned are achieved in embodiments for which the planarwaveguides 2944, the z-pillars 2934 a, 2934 b, the fiducials 2914, andthe alignment aid 2951 are formed from a common planar waveguide layer2905 of the interposer 2904. The formation of each of the alignment aidsfrom the same planar waveguide layer 2905 provides lithographic levelalignment accuracy in the positioning of these alignment aids and to thedevices, die, mounting blocks, and other components of PICs forembodiments that includes alignment aids described herein.

The embodiment of the PIC 2902 shown in FIG. 29A includes patterningsteps for the formation of planar waveguides 2944, the fiducial marks2914 in cavity 2949, z-pillar alignment aids 2934 formed in cavity 2948,z-pillar alignment aids formed for the alignment of a fiber optic cablemounting block in a cavity 2969, and alignment aid 2951, a featurepatterned from planar waveguide layer 2905 that can form a lateralconstraint to restrict lateral movement of a mounted fiber optic cablemounting block and can form all or part of a etch mask for the formationof a cavity 2969 within which all or part of a fiber optic cablemounting block can be mounted. Alignment aid 2951 is formed from theplanar waveguide layer 2905 using a lithographic patterning process topattern a hard mask. The hard mask pattern used to protect the alignmentaid 2951 during an etch step, in some embodiments, is removed with theremoval of the portion of the hard mask used to pattern the planarwaveguides 2944. In other embodiments, the hard mask used to protect thealignment aid 2951 during an etch step is not removed with the removalof the portion of the hard mask used to pattern the planar waveguides2944 but rather is left in place with the other portions of the hardmask that are left in place after the patterning of the planar waveguidelayer 2905, including the z-pillar mask portions, and the fiducial maskportions of the hard mask.

Referring to FIGS. 30A and 30B, additional details of embodiments offiber optic cable mounting blocks that could be used, for example, inthe embodiments described in FIGS. 23-29 are shown. In FIG. 30A(i), anend view of an embodiment of a fiber optic cable mounting block 3062that holds a single fiber optic cable 3054 is shown and in FIG. 30A(ii),is a similar view of an embodiment of a fiber optic cable mounting block3062 that holds two fiber optic cables 3054 is shown. Fiber optic cable3054 resides in recess 3073 a in the base 3064 of the fiber optic cablemounting block 3062 and in recess 3073 b in the lid 3066 of the fiberoptic cable mounting blocks 3062 shown in FIGS. 30A(i) and 30A(ii). Inthese embodiments, the recess 3073 a shown in the base 3064 are av-groove feature. In other embodiments, the recess 3073 a is rectangularin shape. And in yet other embodiments, the recess is semicircular inshape or another shape. And in yet other embodiments, the recess 3073 amay not be present. In the embodiments shown in FIGS. 30A(i) and30A(ii), the recess 3073 b shown in the lid 3066 is a semicircularfeature. In other embodiments, the recess 3073 b shown in the lid 3066is a v-groove feature. In other the embodiments, the recess 3073 b isrectangular in shape. And in yet other embodiments, the recess 3073 b isanother shape. And in yet other embodiments, the recess 3073 b may notbe present. In embodiments, the recesses 3073 a, 3073 b providecontaining function and an aligning function, among other potentialfunctions. The containing function holds, clamps, or otherwise fixes thefiber optic cable in a position that allows for accurate alignment forthe fiber core 3056 at, for example, a reference distance from theinterface of the lid 3066 and the base 3064. The reference distance,“offset” in the embodiments in FIGS. 30A(i) and 30A(ii), shows thedistance from the interface between the lid 3066 and the base 3064 ofthe fiber optic cable mounting block 3062 to the horizontal center ofthe core 3056 of the mounted fiber optic cable 3054. The aligningfunction of the fiber optic cable mounting blocks 3062 provides accuratepositioning of the core 3056 of the fiber optic cable 3054 within thev-groove 3073 a, 3073 b or other shaped recesses in the base 3064 andthe lid 3066. The aligning function of the fiber optic cable mountingblocks 3062 also provides accurate positioning of the core 3056 of thefiber optic cable 3054 relative to one or more of the length, width, anddepth of the fiber optic cable mounting blocks 3062 such that the core3056 can be positioned onto the PIC 3002, for example, on the z-pillars(e.g, 2964), in the fiber cable mounting block cavity (e.g, 2969), incontact with a fiber optic cable mounting v-groove (e.g, 2850), inconjunction with an alignment aid (e.g, 2951) formed from the planarwaveguide layer (e.g, 2905), or in combination with one or more of thesealignment aids or other alignment aid formed on the PIC.

In FIG. 30A(iii), a cross section is shown of fiber optic cable mountingblock 3062 that shows the cross section of the optical fiber 3056. Thefiber optic cable mounting block 3062 is typically configured with anoffset, denoted “lid offset” to accommodate the z-pillars in embodimentsin which z-pillars are utilized to align or contribute to the alignmentof the fiber optic cable mounting block 3062, and one or more of the lid3066, base 3064, and fiber may be held in place with epoxy 3067.

FIG. 30B shows additional detail in the positioning of a fiber cable3054 within a fiber optic cable mounting block 3062 in an embodimentused with z-pillars 3054 to illustrate the alignment of the grooves 3073a, 3073 b. Z-pillars 3054 are formed for example, in a cavity such asthe cavity 2969 shown in FIG. 29B to facilitate wholly, or in part, thealignment of a fiber optic cable mounting block 3062. Z-pillars 3054shows core layer 3058 that is formed from a portion of the planarwaveguide layer (e.g, 405). In embodiments, although the optic signalsin PICs in embodiments do not necessarily propagate in any portion ofthe z-pillars (although not precluded from doing so), optical signals dopropagate in portions of the planar waveguide layer from which theplanar waveguides and other optical features are formed. Thus, in FIG.30B, the alignment of the core 3056 of the fiber optic cable 3054 isshown in alignment with the planar waveguide layer core 3058 present inthe z-pillars 3054, and with the planar waveguide facet 3052 also formedfrom the planar waveguide layer (e.g, 405) shown in the background. Inembodiments, optical signals can be transferred to, or from, or both toand from, the core 3056 of the fiber cable 3054 and the facet 3052 of aplanar waveguide 3044.

It should be noted that in embodiments, the lid 3066 of the fiber opticcable block 3062 typically, although not necessarily, forms the contactwith the substrate to which the fiber optic cable mounting block 3062 isattached as shown in FIG. 30C. This figure shows a (i) cross section and(ii) top down view of an embodiment of a portion of a PIC 3002 for whichthe fiber optic cable mounting block 3062 is aligned with the planarwaveguide core 3058 of planar waveguide 3044. Planar waveguide layer3044 also includes base layer 3059 and top layer 3057 (as described inFIG. 4 , for example). The fiber optic core mounting block 3062 includesthe base 3064 and the lid 3066. Epoxy 3067 a is utilized, for example,to hold together the lid 3066 and base 3064 and to hold fiber opticcable 3054 in the block 3062. The lid 3066 is adhered to the substratewith an epoxy layer 3067 b. In FIG. 30C(ii), the top-down view furthershows an example position of the z-pillar 3054, offset as shown from thefiber cable so that the z-pillars form a contact with the base 3064 ofthe mounting block 3062. Fiducials to facilitate the placement andalignment of the fiber mounting block 3062 are also shown.

The embodiments of the fiber optic cable blocks 3062 shown in FIGS.30A(i) and 30A(ii) are shown in configurations to include one or twofiber optic cables 3054, respectively. Other embodiments are configuredto hold three or more fiber optic cables 3054. In other embodiments,more than two fiber optic cables are included in the fiber opticmounting block 3062. In other embodiments, four fiber optic cables 3054are accommodated in the fiber optic cable mounting block 3062. And inyet other embodiments, three or more fiber optic cables 3064 are mountedin the fiber optic cable mounting block 3062.

In FIG. 30D, an embodiment is shown for a PIC 3002 that is configuredfor a fiber optic cable mounting block 3062 with four mounted fiberoptic cables 3064 (not shown). This figure illustrates a PIC 3002 withwaveguides 3044 in alignment with the v-grooves 3050 formed in thesubstrate of the PIC 3002. Spot size converters (SSCs) have been formedbetween the planar waveguides 3044 and the mounting location for thefiber optic cable mounting block 3062. Also shown in the PIC 3002 arelocations for the mounting or formation of laser devices 3020 and theelectrical contact pads 3030 that form electrical contacts for the laserdevices 3020. In FIG. 30D, four mounted fiber optic cables are providedin the embodiment for the fiber mounting block. In other embodiments,other quantities of fibers may be mounted in the fiber mounting block.And in yet other embodiments, allowances for the positioning andmounting of multiple fiber mounting blocks can be made on an interposersubstrate.

The foregoing descriptions of embodiments have been presented forpurposes of illustration and description and are not intended to beexhaustive or to limit embodiments to the forms disclosed. Modificationsto, and variations of, the disclosed embodiments will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other embodiments without departing from thespirit and scope of the embodiments disclosed herein. Thus, embodimentsshould not be limited to those specifically described herein but ratherare to be accorded the widest scope consistent with the principles andfeatures disclosed herein.

What is claimed is:
 1. A structure comprising a substrate; a firstoptical component on the substrate, wherein the first optical componentcomprises a first optical axis; a first alignment aid element comprisinga first outer surface parallel to a lateral surface of the substrate,wherein the first outer surface is separated by a first distance withthe first optical axis; wherein the first alignment aid element isconfigured for aligning a second optical component with the firstoptical component in a first direction perpendicular to the lateralsurface, a second alignment aid element comprising a pattern on a secondsurface parallel to the lateral surface, wherein the second surface isin a vicinity of the first optical axis in the first direction, whereinthe pattern is configured for laterally aligning a second opticalcomponent with the substrate; a third alignment aid element comprising athird surface not parallel to the lateral surface, wherein the thirdsurface is configured to constrain or guide movements of the secondoptical component in a second direction parallel to the lateral surface.2. A structure as in claim 1, further comprising a fourth alignment aidelement comprising an alignment constraint for laterally aligning anoptical fiber, wherein the alignment constraint is configured to alignan optical axis of the optical fiber with the first optical axis in alateral direction.
 3. A structure as in claim 1, wherein the firstalignment aid element comprises the third alignment aid element, withthe first alignment aid element comprising a pillar comprising the firstouter surface as a top surface and the third surface as a side surface.4. A structure as in claim 1, wherein the third surface is configured toestablish a limit for the second optical component to travel in thesecond direction to be within an alignment tolerance.
 5. A structure asin claim 1, wherein the first distance is configured to match with asecond distance between a fourth outer surface and a second optical axisof the second optical component in a third direction perpendicular tothe second outer surface.
 6. A structure as in claim 1, wherein thethird surface is configured to constrain or guide movements of thesecond optical component in the third direction to a final alignmentposition;
 7. A structure as in claim 1, wherein the third distance isconfigured for a precision placement of the second optical component onthe first alignment aid element for aligning the second optical axis ofthe second optical component with the first optical axis of the firstoptical component in the third direction with a placement accuracy of alithographic process;
 8. A structure comprising a substrate; a firstoptical component on the substrate, wherein the first optical componentcomprises a first optical axis; a first alignment aid element comprisinga first outer surface parallel to a lateral surface of the substrate,wherein the first outer surface is separated by a first distance withthe first optical axis in a first direction perpendicular to the lateralsurface, wherein the first distance is configured to match with a seconddistance between a second outer surface and a second optical axis of asecond optical component in a second direction perpendicular to thesecond outer surface, wherein the first alignment aid element isconfigured for aligning the second optical component with the firstoptical component in the first direction, characterized by aligning thefirst optical axis with the second optical axis in the first direction,when the second component is assembled on the substrate with the firstouter surface contacting with the second outer surface, wherein thefirst alignment aid element further comprises a third surface notparallel to the lateral surface, wherein the third surface is configuredto constrain or guide movements of the second optical component in athird direction parallel to the lateral surface; a second alignment aidelement comprising a pattern on a second surface parallel to the lateralsurface, wherein the second surface is in a vicinity of the firstoptical axis in the first direction, wherein the pattern is configuredfor aligning the second optical axis of the second optical componentwith the first optical axis of the first optical component in the thirddirection.
 9. A structure as in claim 8, wherein the pattern isseparated by a third distance with the first alignment aid element in athird direction parallel to the lateral surface, wherein the thirddistance is configured for a precision placement of the second opticalcomponent on the first alignment aid element with a placement accuracyof a lithographic process during the alignment of the second opticalaxis with the first optical axis.
 10. A structure comprising asubstrate; a first optical component on the substrate, wherein the firstoptical component comprises a first optical axis; a first alignment aidelement comprising a first outer surface parallel to a lateral surfaceof the substrate, wherein the first outer surface is separated by afirst distance with the first optical axis in a first directionperpendicular to the lateral surface, wherein the first distance isconfigured to match with a second distance between a second outersurface and a second optical axis of a second optical component in asecond direction perpendicular to the second outer surface, wherein thefirst alignment aid element is configured for aligning the secondoptical component with the first optical component in the firstdirection, characterized by aligning the first optical axis with thesecond optical axis in the first direction, when the second component isassembled on the substrate with the first outer surface contacting withthe second outer surface; a second alignment aid element comprising afiducial pattern on a second surface parallel to the lateral surface,wherein the second surface is in a vicinity of the first optical axis inthe first direction, wherein the fiducial pattern is separated by athird distance with the first alignment aid element in a third directionparallel to the lateral surface, wherein the third distance isconfigured for a precision placement of the second optical component onthe first alignment aid element for aligning the second optical axis ofthe second optical component with the first optical axis of the firstoptical component in the third direction with a placement accuracy of alithographic process; a third alignment aid element comprising a thirdsurface not parallel to the lateral surface, wherein the third surfaceis configured to constrain or guide movements of the second opticalcomponent in the third direction during a soldering aligning process.11. A structure as in claim 10, wherein the substrate comprises aninterconnection layer disposed on a base structure, wherein theinterconnection layer comprises at least an electrical interconnectionline, wherein the base structure comprises an electrical devicecomprising an electrical terminal connected to the electricalinterconnection line.
 12. A structure as in claim 10, wherein the firstor second optical component comprises a waveguide, an optical device, anoptoelectric device, or a ball lens.
 13. A structure as in claim 10,wherein an optical facet of the first optical component contacts anoptical facet of the second optical component.
 14. A structure as inclaim 10, wherein the first alignment aid element comprises the thirdalignment aid element, with the first alignment aid element comprising apillar comprising the first outer surface as a top surface and the thirdsurface as a side surface.
 15. A structure as in claim 10, wherein thefirst alignment aid element comprises a top layer comprising an etchselectivity as compared to other layers of the first optical component.16. A structure as in claim 10, wherein the first alignment aid elementcomprises a top layer comprising Al, AlOx, Au, Ag, Ni, Pt, Ti, TiOx, Ta,TaOx, while other layers of the first optical component comprise asilicon dioxide, silicon nitride, or silicon oxynitride material.
 17. Astructure as in claim 10, wherein the first alignment aid element andthe second alignment aid element comprise a top hard mask layer formedat a same time with top surfaces of the hard mask layer being the firstouter surface and the second surface.
 18. A structure as in claim 10,wherein the third surface is configured to establish a limit for thesecond optical component to travel in the second direction to be withinan alignment tolerance of less than 2 microns.
 19. A structure as inclaim 10, wherein the third surface is separated with a fifth surface ofthe second optical component by a distance less than 1 micron.
 20. Astructure as in claim 10, a fourth alignment aid element comprising analignment constraint for laterally aligning an optical fiber, whereinthe alignment constraint is configured to align an optical axis of theoptical fiber with the first optical axis in a lateral direction,wherein the fourth alignment aid element comprises a v-groove alignmentaid disposed along the optical fiber.